Wow.
You’ve got a *serious* mess there. How much of the CSS file did you edit yourself – or did it come this way when you downloaded the theme? I see it’s all table-based, as well. You’ve also got some CSS3 stuff in your CSS file – most CSS3 stuff is ignored by most all browsers (save Opera), so it’s being ignored by browsers. (For example, “.clearfix:after” – the :after” is a CSS3 thing. Using it will only work in Opera. So if you’re trying to clear floats or something with it, it ain’t gonna work.)
Personally, if it were me, I’d start over. That’s amazing – I wouldn’t even know where to start on fixing that! (Well, I *would* but that’s actually where my paycheck comes from – fixing entire sites like this!)
You also have a 404 page set as the content for your style.css file – what’s up with that?