Help please - Problem with IE7

Hiya everyone

I have a big problem with my zen cart in IE7 and I was wondering if anyone could point me in the right direction?

When I open my site in IE7 everythings fine untill I add something to the cart. As soon as I do this I lose all of the layout!!

Heres the link:
http://www.provokeshop.com/zen/

Try adding something and see if this happens to you too please

If I empty the cart the site goes back to normal! What could be causing this? Please help if anyone knows

Thanks