I've been thinking about this problem too, especially considering a friend of mine lost his CPU yesterday due to a generic brand pump dying on him. What you'd want to do is rig up a thermistor by the core of the CPU, run to some circuitry that has the ability to cut the AC power to the ATX power supply in the event that the temperature exceeds an insane temp, like say 80c or so.. Set it as high as possible, so it doesn't accidentally trip anytime except the worst case scenario.. Really wouldn't be too hard to do either.. But if you used a relay, the circuit may need a battery backup to keep the AC cut off after the ATX power supply stops feeding power to your temp monitor, and keeping it from turning back on after the temp goes down might be a hassle too. But not impossible.
