Well... You know IE is in quirks mode, right? That comment before the doctype? Unacceptable if you are trying to still support... pretty much ANY IE -- in fact ALL browsers will behave differently than they should thanks to that.
<meta name="generator" content="WordPress 3.0.5" />
Says 99% of what's probably wrong with the code.
It's also knee deep in comments that could be triggering IE and FF rendering errors -- the classic "herpaderp" start comments:
<!-- START: header -->
... no, really? Opening a DIV called header is the start of the header? Followed by the closing comment placement:
<!-- END: header -->
Again, closing the div is the end? No... Much less the reliance on clearing div like it was still 2001... on a page that doesn't need anything fancier than overflow and haslayout to add wrapping behavior. (much less the clearing div being outside #header)
Following this you have nonsensical heading orders, classes on headings for no good reason, a whole slew of pointless extra wrapping DIV making the layout WAY more complicated than need be, paragraphs around non-paragraph elements, static style inlined in the markup, invalid style embeds (that the validator isn't reporting because they're inside CC's) ...
Not entirely surprising you're having problems. The markup pretty much needs to be thrown out and started over clean; and that's BEFORE we even talk about applying style/layout to it with CSS. This is another of those sites where I'm seeing four different layout in six different browsers -- I'm ASSUMING what FF is showing me is what you are aiming for -- it's sure as shine-ola NOT what I'm seeing in Opera, Chrome or IE.