Layout Issue (row gaps)

Hey, got a little problem.

My layout is falling apart in firefox, but displays properly in IE.

I have attempted to move to XHTML but i am still using tables which could be the issue. If you could either tell me a quick solve of this problem or explain how i would go about moving this kind of layout to DIV’s without 2 much difficulty.

the site is here - http://clients.criticalwebdesign.co.uk/americanmarine/

and the rollover css is here - http://clients.criticalwebdesign.co.uk/americanmarine/rollover.css

I thought my code seemed ok, so i don’t hav a clue what is goin on!!

cheers in advance, Andy.