I just DL'd the game, unzipped the archive and tried running it. The first time it worked for the most part but when I tried to play a demo it forced a reboot. Now anytime I try to start the game I get an immediate reboot...bummer

XP Pro SP2 with latest updates
AMD 4200 dual core
1gig single channel
NVidia GeForce 7600GS 512mb with latest update
Game installed on 3rd Sata 2 (non-raid)

now when you say reboot, you mean the computer crashes or it actually says "windows is now shutting down..."

I'd also try running the nexuiz-sdl.exe file and see if you get the same result.

When I say reboot it's straight to BIOS post. I did run it successfully with the nexuiz-sdl.exe.

sounds to me like a strange driver problem. Try updating the nvidia drivers, maybe that will fix it.