I was running into issues where my RadMenu (Sitefinity SiteMenu) would show up behind other elements I had on the page. This issue was only showing up in IE7, not IE8, Firefox, Chrome, Safari etc.
This ended up being related to a problem I had earlier with the RadMenu not staying behind another menu which used the AJAX Control Toolkit hover menu extender. Here is the thread from Sitefinity.com.
Since I had set the RadMenu to position:static, and I had some content lower on the page set to position:relative, the menu was sliding behind that item.
I tried all kinds of different z-index settings on the other content, but couldn't get it to stay behind the menu!
Reading this explanation of z-index led me to try some other position settings. Eventually thinking that relative was causing a higher z-index than my menu (which should have been already set very high), logic says using position:static would put it back down to something likely in the single digits.... and of course I was reminded this was how I had to fix the RadMenu vs. hover menu extender issue. No z-index setting was necessary.