IE problem with divs and z-index

[jromao]

Hey all \o/

I'm currently finishing a website and I've made a pure CSS dropdown menu. But there's a small problem with it...

The menu, which is supposed to have submenus with some links (of course), is on the top part of the design. And all that area is composed by 3 parts, the top part (only some images with a degradé), the body part of the header (where the menu is actually staying) and the footer part of the header.

Everything is ok on on Opera and Chrome but, in the all mighty IE7, the footer div stays on top of the submenus even though it as a z-index of -1...
Doesn't z-index work on IE?
How can I solve this

<snip>

[edited by: swa66 at 7:07 pm (utc) on Feb. 4, 2009]
[edit reason] No URLs, please post minimal code showing the problem instead [/edit]

[oluoch28394]

some code might help you get help.

[jromao]

didn't notice that the code link had been taken
The body of the header:

.tabelasd {
 position: relative;
 height: 110px;
 background: #222222 url(http://example.com/image.gif) repeat;
}

The footer:

.fundosd {
height: 58px;
line-height: 58px;
padding-top: 0px;
margin: 0;
background: url(http://example.com/image.gif) 0 0 repeat-x;
z-index:-1;
}

The submenus

#menu li ul {
margin:0px;
display:none;
position:absolute;
left:0px;
top:33px;
}
#menu li:hover ul {
display:block;
width:100px;
}

2 Images (1st-> scheme of the page, 2nd->comparison of the submenus between opera and IE)
Edit: Can I at least put links to 2 images?

[edited by: swa66 at 9:19 pm (utc) on Feb. 6, 2009]
[edit reason] no URLs, please see ToS and forum charter [/edit]