It's a pretty simplistic site, but not an altogether bad one. I've certainly seen far worse, and while it's not the most flashy thing on the planet that's far better than adding loads of crap that makes the thing hard to navigate.
However, assuming you wrote the HTML yourself it is questionable. Tags should all be in lower case these days for a start. And beyond that, you should really be validating all the HTML you use (if it's valid then all browsers should display it properly - and if they don't it's bugs with the browser, not you.)
As you can see from your validation check here
, you've got quite a bit of work to do if you want it to validate! And that's just with HTML4. These days you should really be aiming for validation using XHTML strict, and if that's the case...