Internet Explorer 6 & 7 no text decoration:border-bottom

[VMarv]

Hi there

Trying to get to grips with css and have this site I have uploaded to test at: http://www.trucreative.co.uk/Lugo_2009/index.htm is a bit of a fuse between tables & css as I couldn't get my head round columns. But renders well in Firefox and Safari and IE8. The problem is that in Internet explorer 6 & 7 it is not showing the underline on the navigation at the top and bottom of the page. Any help with this would be greatly appreciated - why can't IE just WORK!!...:confused:

The CSS is:
.underlinemenu{
font-family: "Trebuchet MS", Helvetica, Verdana, sans-serif;
font-size: 12px;
font-weight: bold;
color: #FFFFFF;
width: 100%;
}

.underlinemenu ul{
padding: 10px 15px 3px 50px;
margin: 0;
text-align: left;
}

.underlinemenu ul li{
display: inline;
}

.underlinemenu ul li a{
color: #FFFFFF;
padding: 10px 15px 3px 3px;
margin-right: -4px;
text-decoration: none;
border-bottom: 3px solid;
border-bottom-color:#AAC3AB;
}

.underlinemenu ul li a:hover, .underlinemenu ul li a.selected{
border-bottom-color:#F50003;
}