HTML - How To Make A Dropdown Box Link To Other Pages

//Display the categories
 $sql = "SELECT            
		categoryID,
		categoryName,
		categoryDescription
        FROM
            categories";
                 
                $result = mysql_query($sql);
                 
                echo 'Select Category:';    
                 echo '<select name="Categories">';
                 while($row = mysql_fetch_assoc($result))
                  {
                       echo '<option value="' . $row['categoryID'] . '">' . $row['categoryName'] . '</option>';
                  }
                  echo '</select><br />'; 
                 
                  '</form>';

//Displaying the topics
 $sql = "SELECT    
		topicID
		topicSubject,
		topicDate,
		topicCategory,
		topicByUser
        FROM
            topics";
                 
                $result = mysql_query($sql);
                 
                echo '<form method="post" action="">
                                 Select Topics:'; 
                
                                
                 echo '<select name="topicSubject">';
                 while($row = mysql_fetch_assoc($result))
                  {
                       echo '<option value="' . $row['topicID'] . '">' . $row['topicSubject'] . '</option>';
                  }
                  echo '</select><br />'; 
                   
					//submit button
                  echo ' <input type="submit" value="Delete topic" name="submitButton" />
				  
 
                  </form>';

<form method=post action="http://links.verotel.com/cgi-bin/addreseller.verotel" target=_blank>
<input type=hidden name=verotel_website value=80145>
<center><input type=submit value="Sign me up!">
</center>
</form>