你有没有在UL标签上使用IFrame垫片？

I ahve a menu structure that uses UL and LI elements to drop down from a main menu. The problem i am having (of course) is in IE6 where the menu drops behind SELECT elements despite the z-index. I have tried adding an IFram shim to the UL which contains the LI elements which are the menu items. The problem is the Shim sits on top of the UL instead of behind it despite the fact the shim has a lesser z-index than the UL element. I ahve a menu structure that uses UL and LI ele