Menubar seperator in YUI menu

Hi all,
I'm quite new to CSS. I tried to design a top-navigation using yui 2.6 menu from markup. Things work fine. But I wanted to create a sperator to group the menubar items. So I added a new class in css like

.yui-skin-sam .yuimenuitem-seperator{
_border-bottom:solid 1px #fff;
background-color:#ddd;
height:1px;
}


This works fine with Firefox not in IE...( IE as usual.... )

Anyone please suggest me the right way to use seperators in menubar items using YUI..

Best regards,
Markish

http://markishonline.com