Aha. There are two big clues here (easy to spot now that I've seen the site!) but should have been obvious to me just from what you'd written already:1. the difference between IE and Mozilla which usually indicates that the page's structure is broken and the browsers are trying to deal with it in different ways
2. that it's better when you click on a category, which implies that it's something specific to the main page.Sure enough, the site fails validation and has a number of illegally placed tags as well as tags being closed that aren't open.
A check of the HTML being displayed on the front page shows that it's a mess of nested and redundant tags, and I suspect that IE thinks that the page finishes earlier than you intend it to.
I also suspect that if you clear up the code generating that block in the center column, your problems will just melt away.