yeah you are right, the site looks fine and works great in Mozilla but when it comes to IE it looks like this: http://i36.tinypic.com/ic1vf7.jpg
You might want to make a separate IE stylesheet (included with a conditional statement) and reduce the padding on that menu.
Ain't sure about the screen shot but in IE6 its exhibiting similar bad behavior. Guess its using PNGs for the top menu, the nav below the header is spilling over. side nav is pushed down.
God I hate IE. Even if you make the website work with IE7, IE6 and below have problems.... I think I'll ignore IE6 problems as IE 8 will be out soon too, and people should be upgrading anyways.
If you're going to use a version of IE to fix, it's best to use version 6. That's because if you do version 6, usually all of the issues in 6 & 7 will be solved. However, if you only do 7, then there will still be many in 6.
i should run a script on my site to see how many people are using IE6 i actually just looked at my Google Analytics and 25% of the 55% that use IE , have IE 6.