PHP - Need Information To Stay In Fields After Page Refresh..

When someone types in thier information in my Sign Up form i want the information they entered to stay after the page refresh.

For example: I type in my information, but in the email field i forget the '@' symbol and then hit "Sign Up". Then the page would refresh and i would get an error message saying "You must enter a valid email address!" and all the information i typed in before would be gone and i'd have to start over with everything..

My question is, how can i make so that all the information I entered stays after the page refresh? Is there a simple way to do it or do I have to rewrite all my code? (i've provided it below)

I know that you can use jQuery, AJAX and JS to acomplish this and also show the error message without refreshing the page but I don't know much about that and i'm trying to use as little JS as I can. So if there is another easier way?

Here is my PHP script that holds the validation process and shows the errors etc:
<?php

class Register
{
  private $username;
  private $first_name;
  private $last_name;
  private $password;
  private $passmd5;
  private $email;
  private $confemail;
  private $gender;
  private $birth_month;
  private $birth_day;
  private $birth_year;
  private $iagree;

  private $errors;
  private $token;

  public function __construct()
  {
    $this->errors = array();

    $this->username     = $this->filter($_POST['username']);

$this->first_name   = $this->filter($_POST['first_name']);

$this->last_name    = $this->filter($_POST['last_name']);
    $this->password     = $this->filter($_POST['password']);
    $this->email        = $this->filter($_POST['email']);

$this->confemail    = $this->filter($_POST['confemail']);

$this->gender       = $this->filter($_POST['gender']);

$this->birth_month  = $this->filter($_POST['birth_month']);

$this->birth_day    = $this->filter($_POST['birth_day']);

$this->birth_year   = $this->filter($_POST['birth_year']);

$this->iagree       = $this->filter($_POST['iagree']);
    $this->token        = $_POST['token'];

    $this->passmd5      = md5($this->password);
  }

  public function process()
  {
    if($this->valid_token() && $this->valid_data())
         $this->register();

    return count($this->errors)? 0 : 1;
  }

  public function filter($var)
  {
    return preg_replace('/[^a-zA-Z0-9@.]/','',$var);
  }

  public function register()
  {
   mysql_connect("localhost","root","") or die(mysql_error());
   mysql_select_db("membership") or die (mysql_error());

   $sql = "INSERT INTO users(username,password,first_name,last_name,email,gender,birth_month,birth_day,birth_year) VALUES ('{$this->username}','{$this->passmd5}','{$this->first_name}','{$this->last_name}','{$this->email}','{$this->gender}','{$this->birth_month}','{$this->birth_day}','{$this->birth_year}')";

mysql_query($sql) or die(mysql_error());

   if(mysql_affected_rows()< 1)
     $this->errors[] = "Could Not Process Form";
  }

  public function user_exists()
  {
    mysql_connect("localhost","root","") or die(mysql_error());
    mysql_select_db("membership") or die (mysql_error());

    $data = mysql_query("SELECT username FROM users WHERE username = '{$this->username}'");

    return mysql_num_rows($data) > 0 ? 1 : 0;
  }

  public function show_errors()
  {

    foreach($this->errors as $key=>$value)
      echo "<div class=errormessages> 

$value

</div>

<br />";
  }

  public function valid_data()
  {
    if ($this->user_exists()){
      $this->errors[] = 'The username is already taken, choose another one!';
      }

if (empty($this->username)){
      $this->errors[] = 'You must enter a username!';

  }

if (empty($this->first_name)){
      $this->errors[] = 'You must enter your first name';

  }

  
    if (empty($this->password)){
      $this->errors[] = 'You must enter a password!';

  }

elseif (strlen($this->password) < 6){

  $this->errors[] = 'Your password must be longer than 6 characters!';

  }

    if (empty($this->email)){
      $this->errors[] = 'You must enter an email address!';

  }

elseif (!preg_match('/^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z]{2,4}$/',$this->email)){

  $this->errors[] = 'You must enter a valid email address!';

  }

elseif ($this->email != $this->confemail){

  $this->errors[] = 'The email addresses you entered did not match!';

  }

if (empty($this->birth_month)){
      $this->errors[] = 'Select which month you were born!';

  }

if (empty($this->birth_day)){
      $this->errors[] = 'Select which day you were born!';

  }

if (empty($this->birth_year)){
      $this->errors[] = 'Select which year you were born!';

  }

if (empty($this->iagree)){

  $this->errors[] = 'You must agree to the <a href="#">Privacy Policy</a> and <a href="#">Terms of Use</a> to sign up!';

  }

  return count($this->errors)? 0 : 1;
  }


  public function valid_token()
  {
   if(!isset($_SESSION['token']) || $this->token != $_SESSION['token'])
     $this->errors[] = "Invalid Submission";

   return count($this->errors)? 0 : 1;
  }
}

?>

And here the HTML form:
Code: [Select]
<?php
session_start();

if(isset($_POST['register']))
{
  include_once('classes/class.register.php');

  $register = new Register();

  if($register->process())
    echo "Successfully Signed Up!";
  else
    $register->show_errors();
}

$token = $_SESSION['token'] = md5(uniqid(mt_rand(),true));
?>



<!doctype html>
<html>
<head>

<link rel="stylesheet" type="text/css" href="css/main.css">
<link rel="stylesheet" type="text/css" href="css/register.css">
<script type="text/javascript" src="js/passwordmeter.js"></script>

</head>
<body>

<script src="jquery.js"></script>

<div class="center">

<!-- PHP -->
<?php require("html/menu.inc"); ?>
<?php require("html/layout.inc"); ?>
<?php require("html/login.inc"); ?>
<!-- PHP -->

<div class="register">
<header>Sign Up Now!</header>
<form method="POST" action="<?php echo $_SERVER['PHP_SELF'];?>">
<ul>
<li>
<label for="username">* Username: </label><br />
<input name="username" autofocus="on" class="rusernamefield" type="text"></input>
</li>
<li>
<label for="first_name">* First Name: </label><br />
<input name="first_name" class="rfirstnamefield" type="text"></input>
</li>
<li>
<label for="last_name">Last Name: </label><br />
<input name="last_name" class="rlastnamefield" type="text"></input>
</li>
<li>
<label for="password">* Password: </label><br />
<input name="password" class="rpasswordfield" onkeyup='password_strength(this.value)'></input>
</li>

<div id="password_strength_border">
<div id="password_strength" class="strength0"></div>
</div>

<li>
<label for="email">* Email Address: </label><br />
<input name="email" class="remail" type="email" placeholder="email@address.com"></input>
</li>
<li>
<label for="confemail">* Confirm Email Address: </label><br />
<input name="confemail" class="rconfirmemail" type="email" placeholder="email@address.com"></input>
</li>
<li>
<label for="gender">* Gender: </label><br />
<select name="gender">
<option value="Man" selected="selected">Man</option>
<option value="Woman">Woman</option>
</select>
</li>
<li>
<label for="birth_month">* Birth Day: </label><br />
<select name="birth_month">
<option disabled="disabled" selected="selected">Month</option>
<option value="01">January</option>
<option value="02">February</option>
<option value="03">March</option>
<option value="04">April</option>
<option value="05">May</option>
<option value="06">June</option>
<option value="07">July</option>
<option value="08">August</option>
<option value="09">September</option>
<option value="10">October</option>
<option value="11">November</option>
<option value="12">December</option>
</select>
<select name="birth_day">
<option disabled="disabled" selected="selected">Day</option>
<option value="01">1</option>
<option value="02">2</option>
<option value="03">3</option>
<option value="04">4</option>
<option value="05">5</option>
<option value="06">6</option>
<option value="07">7</option>
<option value="08">8</option>
<option value="09">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
<option value="13">13</option>
<option value="14">14</option>
<option value="15">15</option>
<option value="16">16</option>
<option value="17">17</option>
<option value="18">18</option>
<option value="19">19</option>
<option value="20">20</option>
<option value="21">21</option>
<option value="22">22</option>
<option value="23">23</option>
<option value="24">24</option>
<option value="25">25</option>
<option value="26">26</option>
<option value="27">27</option>
<option value="28">28</option>
<option value="29">29</option>
<option value="30">30</option>
<option value="31">31</option>
</select>
<select name="birth_year">
<option disabled="disabled" selected="selected">Year</option>
<option value="2011">2011</option>
<option value="2010">2010</option>
<option value="2009">2009</option>
<option value="2008">2008</option>
<option value="2007">2007</option>
<option value="2006">2006</option>
<option value="2005">2005</option>
<option value="2004">2004</option>
<option value="2003">2003</option>
<option value="2002">2002</option>
<option value="2001">2001</option>
<option value="2000">2000</option>
<option value="1999">1999</option>
<option value="1998">1998</option>
<option value="1997">1997</option>
<option value="1996">1996</option>
<option value="1995">1995</option>
<option value="1994">1994</option>
<option value="1993">1993</option>
<option value="1992">1992</option>
<option value="1991">1991</option>
<option value="1990">1990</option>
<option value="1989">1989</option>
<option value="1988">1988</option>
<option value="1987">1987</option>
<option value="1986">1986</option>
<option value="1985">1985</option>
<option value="1984">1984</option>
<option value="1983">1983</option>
<option value="1982">1982</option>
<option value="1981">1981</option>
<option value="1980">1980</option>
<option value="1979">1979</option>
<option value="1978">1978</option>
<option value="1977">1977</option>
<option value="1976">1976</option>
<option value="1975">1975</option>
<option value="1974">1974</option>
<option value="1973">1973</option>
<option value="1972">1972</option>
<option value="1971">1971</option>
<option value="1970">1970</option>
<option value="1969">1969</option>
<option value="1968">1968</option>
<option value="1967">1967</option>
<option value="1966">1966</option>
<option value="1965">1965</option>
<option value="1964">1964</option>
<option value="1963">1963</option>
<option value="1962">1962</option>
<option value="1961">1961</option>
<option value="1960">1960</option>
<option value="1959">1959</option>
<option value="1958">1958</option>
<option value="1957">1957</option>
<option value="1956">1956</option>
<option value="1955">1955</option>
<option value="1954">1954</option>
<option value="1953">1953</option>
<option value="1952">1952</option>
<option value="1951">1951</option>
<option value="1950">1950</option>
<option value="1949">1949</option>
<option value="1948">1948</option>
<option value="1947">1947</option>
<option value="1946">1946</option>
<option value="1945">1945</option>
<option value="1944">1944</option>
<option value="1943">1943</option>
<option value="1942">1942</option>
<option value="1941">1941</option>
<option value="1940">1940</option>
<option value="1939">1939</option>
<option value="1938">1938</option>
<option value="1937">1937</option>
<option value="1936">1936</option>
<option value="1935">1935</option>
<option value="1934">1934</option>
<option value="1933">1933</option>
<option value="1932">1932</option>
<option value="1931">1931</option>
<option value="1930">1930</option>
<option value="1929">1929</option>
<option value="1928">1928</option>
<option value="1927">1927</option>
<option value="1926">1926</option>
<option value="1925">1925</option>
<option value="1924">1924</option>
<option value="1923">1923</option>
<option value="1922">1922</option>
<option value="1921">1921</option>
<option value="1920">1920</option>
<option value="1919">1919</option>
<option value="1918">1918</option>
<option value="1917">1917</option>
<option value="1916">1916</option>
<option value="1915">1915</option>
<option value="1914">1914</option>
<option value="1913">1913</option>
<option value="1912">1912</option>
<option value="1911">1911</option>
<option value="1910">1910</option>
<option value="1909">1909</option>
<option value="1908">1908</option>
<option value="1907">1907</option>
<option value="1906">1906</option>
<option value="1905">1905</option>
<option value="1904">1904</option>
<option value="1903">1903</option>
<option value="1902">1902</option>
<option value="1901">1901</option>
<option value="1900">1900</option>
</select>
</li>
<li>
<label for="iagree" class="iagreetext">*  I Agree to the <a href="#">Privacy Policy</a> and <a href="#">Terms of Use</a></label>
<input name="iagree" type="checkbox" class="iagreebox"></input>
</li>
<input name="register" class="registerbutton" type="submit" value="Sign Up"></input>
<p class="fieldsmarked">Fields marked with an (*) is required</p>
<input type="hidden" name="token" value="<?php echo $token;?>"/>
</ul>
</form>
</div>

</div>

</body>
</html>