I had the same problem with mine. It's an AMD Athelon 64 x2. Found this site
though, and since doing what it said I've been able to play for the past 4 hours. With sound and everything, although I did turn the graphics quality to medium because of the seperate issue with NVIDIA cards.
Don't get me wrong, I like lucasarts, I just wish that once in a while they would release a game that's actually finished. (I'm still waiting for the other half of KOTOR II). I mean, not supporting the next generation of cpu's, or the most popular video cards available, that seems a little sloppy. And when I asked them about it, all I got was "yeah, we know, keep an eye out for a patch...eventually". In other words, may the force be with you, since we won't be.