Cross-Browser Compatibility

I am in the process of creating a WordPress template for a client. I am currently stuck at cross-browser compatibility, as the website breaks in IE6 and 7. I need someone who has experience in compatibility to take a look at my code and identify which areas are causing my problems. There are currently two issues in IE 6 and one in IE7, both are related to positioning of the sidebars. I have cleared out a significant number of bugs, but I am completely stuck on these. I am using the Wordpress framework Thematic to construct my theme, and, as near as I can tell, this framework behaves properly in IE6 out of the box, so I have done some small thing to it that is causing a major problem. I suspect that it has something to do with the column math not quite adding up, but all of the solutions I have tested have yielded nothing. The website is: [login to view URL]