Problems with z-index or positioning with IE5

[Carpy]

Im using the below CSS that was provided by a member on this forum. It works great. However I have one problem.

The idea is to center the webpage and to allow absolute position so I can shift the important content up the code for SEO purposes.

However im also using OpenCubes Infinite menu within the topnav <DIV>, using IE5 the dropdown menus fall below the centcol, cookiecrumb and h1 <DIV>s. This work correctly in IE7

I know it is something to do with the #frame_outer or #frame_inner div as when these are removed the dropdown menu works fine, however all my absolute positions and center positioning is removed. Can anyone see a prblem with the below code that may be causing this.

Thanks

#frame_outer, #frame_inner, #header, #h1container, #h1, #topnav, #cookiecrumb, #centcol, #rghtcolcontain, #footer{
position : absolute;
left: 582px;
background-color: #FFFFFF;
top: 161px;
overflow: visible;

}
#frame_outer {top : 10px; left : 0; width : 100%; padding : 0; margin : 0; background-color: #FFCC00;}
#frame_inner {top : 0px; left : 50%; width : 729px; height : auto; margin: 0 auto 0 -365px; background-color: #fffff;}

[Carpy]

Any ideas?
Im stuck on this :(