please help me (css hell with IE7)

can someone please help me out here? ??

my dropdown looks good in IE8, FF, Chrome
https://img638.imageshack.us/img638/539/ie8ffchrome.jpg

In IE7, dropdown is behind parent category
https://img704.imageshack.us/img704/7793/ie7i.jpg

CSS:

#dropmenu, #dropmenu ul {margin:0; padding:0; list-style-type:none; list-style-position:outside; position:relative; line-height:1.5em; z-index:400; background:#f2f5f7; font-weight:bold; float:left;} 

#dropmenu a {display:block; padding:0.25em 1em; color:#08586a; border-right:1px solid #c8c8c8; text-decoration:none; background:#f2f5f7;}
#dropmenu a:hover {background:#006c85; color:#fff;}
#dropmenu li {float:left; position:relative;}
#dropmenu ul {position:absolute; display:none; width:12em; top:1.4em; left:-1px;}
#dropmenu ul a {border-left:1px solid #fff;}
#dropmenu li ul {border-top:1px solid #fff; width:14.1em;}
#dropmenu li ul a {width:12em; height:auto; float:left;  border-bottom:1px solid #08586a; background:#08586a; color:#fff;}
#dropmenu ul ul {top:auto;}
#dropmenu li ul ul {left:12em; margin:0px 0 0 10px; }
#dropmenu li:hover ul ul, #dropmenu li:hover ul ul ul, #dropmenu li:hover ul ul ul ul {display:none;}
#dropmenu li:hover ul, #dropmenu li li:hover ul {display:block; }

Full CSS: https://www.itera.ee/wp/wp-content/themes/bcs/style.css

This should be relatively easy to fix with z-index, but where do i need to stick it?