Seems to me like the tables are stretching your page. I had the same problem with one of my websites. Play about with your table sizes and see what you come up with. Good luck! Scott.
You aren't going to like my answer... The offending part of the code is it's entirety. 451 validation errors spells that out. XHTML 1.1 doctype mandates the XML prolog - which you don't have because that would throw IE into 'quirks mode' - so it's invalid XHTML right out of the gate, at least drop it to XHTML 1.0 Strict. (1.1 should never be deployed for a live public access website because it's not ready for primetime in terms of browser support) no namespace on the HTML tag - invalid XHTML use of tags that don't even exist in the X1.1 specification (like CENTER) and are deprecated in most other modern 'strict' specifications. Likewise the use of attributes like 'target' which are ALSO invalid in XHTML strict doctypes. Use of tags that don't even EXIST outside Nyetscape 4 - ILAYER??? Use of a table for a single column - /FAIL/ at intarweb. Nasty case of excess containers and classitus. No signs of anything resembling semantic markup. HORDES of inlined presentation. improperly written attributes for the XHTML doctype. (like the lack of quotes around attribute values) We're talking 73k of HTML and 18k of css for 7k of text content - WORST CASE the page shouldn't be more than 40k COMBINED. Topping it off, baby sized fonts that make most users dive for the zoom control to even read them combined with 822k in 129 files - I know broadband users that won't wait that long for shit to load. We're talking over 40 seconds page load for a T1 user - **** that. My advice - chuck it and start over - possibly getting someone who understands HTML/CSS to write it for you.