If you are experiencing any problem with Nvidia cards, go to Display Properties>Geforce 4 Tixxx>Performance and Quality Settings and set your Peformance tab to APPLICATION.
I'm really loving this game, so far its been the best single player experience in a long while. On a Geforce 4 Ti4600 at 800x600 with everything set to maximum, it looks really gorgeous, surely must kick bellybutton with a Radeon 9700 Pro.