You have a few errors in your code - they don't look like they're the reason, but they could be:
Also, in IE there's a --> at the very top and another one to the right of the pink-ish table. I don't see any messed up comments - but maybe you can't have the / in them... who knows. Little issues like this can often mess up a design.
Also, just to point out another issues - in IE6, the next and previous buttons disappear when you hover over them.
Fix up some of those errors and see if it helps at all. Then post back here.
You can also look up IE hacks (google it)... there's a bunch of ways to set up your css so that only IE reads certain parts - or so that IE ignores a section. It's sometimes helpful when you can't get around certain issues.