Computer restarts only when playing games

All,

I am running Windows XP with service pack 3
AMD Athlon XP 3200+ 2.07 GHz, 1GB of Ram.
NVIDIA GeForce 6200 graphic card.

The PC is very stable when I am using the internet/listening to music and has never restarted unexpectly during this type of use.
However, when I attempt to run a game (e.g Civilization IV, Sid Meiers Pirates or Star Wars Empire) the game will load and allow me to play for a while but then the entire system will re-boot.

Can anyone give me some tips on how I can trace the problem?
Thanks
M Mannas

ok heres what i think your problem is, your cpu is probably over heating which causes the computer to re-boot, it re-boots the computer because it would fry otherwise, another problem might be your powersupply, also check inside your tower for any dust and in your heatsink and fan, remove all dust completly first before doing anything else for that might be the main casue of the overheating of your cpu

yeah, i too think something is overheating, try these heat monitors

Speedfan, Motherboard Monitor, & Hardware Monitor

take the average of all 3 because temp detection software is generally not very reliable as the only means of detecting temp