Z-Index: Divs still overlap in the wrong order (browserwide)

I can't select one of those dropdrown-links, although the #header div has a higher z-index than the rest. All relevant divs are in the same level but do not align properly:http://img32.imageshack.us/img32/4245/zindex.png\[code\] <div id="header"> <div id="navigation"> </div> </div> <div id="sidebar"></div> <div id="content"> ... </div>#header { width: 915px; height: 76px; z-index: 5;}#content { width: 677px; height: 412px; margin-left: 202px; z-index:1;}#sidebar { float: left; width: 200px; height: 448px; z-index: 2;}#navigation { height: 28px; width: 915px; float: right; }\[/code\]
 
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