you could also optimise the images for the buttons, i got one of them down to 1.6k from 2.05k before any visible loss of quality occurred. it doesn't sound like much but ther's a lot of images on your page so it all adds up and will help the page load faster.
Rollovers would make them look nicer but this would add the the page load time and slow it down even more.
also, all the text on your home page is actually images. You'll need to get some good keyword dense text on to your pages as this will help you achieve high rankings in the search engines.
hope this helps,
Dave