This is why you should not but "indy" games.
I've never been much of a cheerleader, but I have to say that the best and most detailed support on this issue has come from Stardock from what I've seen. This thread was started by Stardock, being very honest and upfront about the problems. It's encouraged me to definitely buy more Stardock, if not "indy" games in general.
This is the first major issue I've had with a Stardock product and it's not even their fault. Does anyone else here remember the hell that was CivIII, a "mainstream" game, right out of the box?
The word on the message boards is NVidia drivers. Ok, I can deal with that. After two beta releases and one formal release of NVidia drivers, the game still crashes.
Other games work, Supreme Commander, etc. It is silly to just blame this on the driver. The other games have found a way to work, this game should also.
I'm glad your experience with your games has been much smoother than mine. I have two games that won't run and another handful that don't run optimally. Having to turn off advanced graphics options so that the game will even run is not my idea of a good gaming experience.
I recommend you do a search for information on nVidia drivers on Vista out there on the interwebs. You'll find this problem is much larger than just GC2 - don't forget to check out the site talking about the class action lawsuit.