The biggest question is going to be what kind of video card you have, and possibly which drivers you're using for it. The Nvidia 8800 is the worst of them all -- no one has yet managed to figure out how to get MTW to run with it (at least not that anyone's admitted so far) -- and the whole 8000 series in general has been known to give people trouble, although there are a couple solutions that have worked for some people.

If you *do* have an Nvidia (and and it's not the 8800), I urge you to check out this thread in the Main Hall, if you've not already done so. One of the simplest solutions for a lot of people (including myself) was to just roll back to an earlier set of video drivers. You might not necessarily have it that easy, of course, but it's still worth taking a look.