I've run repair installations of the game (Call of Duty 4) and made certain the drivers for my vid card are updated. I've run the game in safe mode, and still it crashes. I'm running Vista 64-bit and I've got a GE Force GT220 1 gig card in the machine, and wondering if it's the problem, as the machine is about 4 years old now. I've opened the case, vacuumed the dust out. I've also scanned my machine for malware, using the tools I'm learning in Geek U, and the logs have come out clean.
One other thing: Every time the machine reboots, the Steam client tries to update itself. I've also run repair installations on that software as well, but it continues to try and update itself whenever the game crashes.