CSS - Overlaying One Div On Top Of Another Div

Hi all,

I am looking for information on overlaying a form over a site. You see this technique used for advertisements and the like, generally in flash.

Most of what I am finding is suggesting the z-index using div tags, and I am looking to corroborate that.

Any information or links to good examples or tutorials would be great.

Thanks
Caden

I can't get my css image overlay working for my header.

This is what I have:
Code:

   #header{
         background: #000 url("header_tile.gif") repeat-x;
         margin: 0px;
         padding: 0px;
         height: 143px;
         font-size: 7pt;
         font-weight: bold;
         position: relative;
        }

        #header #mainlogo {
         background: #000 url("main_logo.png") no-repeat;
         position:absolute;
         top:0px;
         left:0px;
         z-index:5;
        }
 

I can't seem to get it the mainlogo class to display at all. How would I write my div's to get this working.

I tried this but it didn't work:
Code:

   <div id="header">
      <div id="mainlogo">

      </div>
   </div>
 

Thanks,
Laura

Can someone help me with stopping the sidebar from overlapping the footer on jussbuss.tv singles category section, please help

The main things I can point out a
Can't seem to get the logo to over lap. Can't seem to get FF to recognize the margins, but somehow IE can.
There are other problems but those are the main two.

I need to get this:

http:// devbum. com/coded/audven/

to look like this:

http:// devbum. com/coded/audven/audven.png

Any help is greatly appreciated!

I know I'm not supposed to post links but there really is no other way to receive help with this problem otherwise.