It looks fine on my computer (win vista 64bit, firefox 3.05) but there are at least 24 errors in the code (according to HTMLTidy) so perhaps if you can iron these out it will display better across platforms. Use the W3C validator to remove the errors.
Have you any idea which OS and browsers the people with problems were using?
Update It also looks fine on ubuntu 8.0.4, firefox 3.01
Unrelated to your question, but the homepage photo looks quite blurry, and I see from its properties that it is a smaller image scaled up. This seldom produces acceptable looking results, and you should replace it with a correctly sized image if possible. After all, your home page is your best chance to make a good impression!