greenbay v2

I’m using this theme for the website of my local political party ( https://www.groenlinks-noo.nl ), but I just noticed something wrong with it in IE6. I’m using Firefox myself, so thats why I hadn’t noticed it before.
The right colum moves under the postings in IE6. And I’ve no idea how to solve that. In the style.css they’re talking about a container (but that’s the whole thing), about mainleft (probably the part with the postings?) and mainright (the navigation-bar?). But I don’t see the value of the size of the mainleft and -right anywhere. Can it be the fact the the mainleft and- right have a ‘float’ value in them???

Hopefully this is a bit of a clear story for experienced people. ??

#container
{
width: 750px;
height: 100%;
margin: 0 auto 20px auto;
background: #F4F4F4;
border: 1px solid #677E43;
background-color: #f4f4f4;
}

#mainleft
{
color: #3A4925;
margin-top: 10px;
padding: 5px;
padding-bottom: 10px;
padding-right: 10px;
line-height: 175%;
width: 480px;
float: left;
margin-left: 20px;
text-align: justify;
}

#mainright
{
margin-right: 10px;
width: 150px;
float: right;
line-height: 175%;
margin-left: 0px;
margin-top: 10px;
text-align: left;
}