If you try to use Z-index with Internet Explorer (I hear this is a problem on both 6 and 7), you may have problems getting it to “listen” when Firefox seems to handle z-index just fine.
The problem is a bug in IE which does not render z-index properly all of the time. If you just use z-index: XXX and do not have a position tag, then it does not work. By adding “position: relative” or “position: absolute” tag to your CSS div tag, it magically works!
Thanks for wasting several hours of mine IE.