Problem with layout in IE6 (and Firefox)

I’m working on a new layout for my website, and I just ran it through browsercam to see how it held up.

It works on [URL=”http://www.therandomplanet.com/ie7.jpg”]IE7[/URL], which is what I’m using, and (strangely enough) [URL=”http://www.therandomplanet.com/ie4.jpg”]IE4[/URL], but not IE5 or [URL=”http://www.therandomplanet.com/ie6.jpg”]6[/URL], or [URL=”http://www.therandomplanet.com/ff.jpg”]Firefox[/URL]. (but I knew that already)

I’m not really bothered about IE5, but I would like it to run on IE6. Here’s the page itself (only the indexpage is up at the moment, and the others don’t have the same layout, anyways):

[url]http://www.therandomplanet.com/planet.html[/url]

and the stylesheet:

[url]http://www.therandomplanet.com/default.css[/url]

Does anyone have any idea how I can fix it for IE6? It’s probably some silly, minor thing, but I don’t have the skills to figure it out. I didn’t write the CSS itself (edited it, though, which may be where I broke it), and the website I got it from is down, but this is the [URL=”http://www.therandomplanet.com/template/index.html”]original layout[/URL] and [URL=”http://www.therandomplanet.com/template/style/default.css”]stylesheet[/URL].

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