Something wicked in IE6 and IE7

I haven’t checked my site in a long time, but today I checked it in IE6 and IE7 and it looks like a complete mess - http://mtsix.com/

The styles are http://mtsix.com/wp-content/themes/mt3/new_ie.css and http://mtsix.com/wp-content/themes/mt3/newstyle.css

I remember I once developed it so that it looks okay in IE, and I haven’t changed anything since. It looks like some overflow:hidden; is causing problems for sure, maybe something else. Does anyone know what could be causing it?