Hmm, yeah, overclocking won't help your system, so I would take them off since it seems its unstable, even if it works while playing things, it doesn't when you exit.
When yuo minimize a game, and exit a game, it's the RAM that struggles to bring everything back, and it might be your RAM that is causing it to crash and restart, and if you were ovcerclocking, I might note that PC3200 RAM isn't that good for it anyway, and might have become unstable and crashed because it couldn't keep up when it needed the power most (when exiting).
So I would take off all overclocks and test, if that works, then maybe increase it a little bit (about 5mhz increments) until it becomes unstable.
If taking it off overclock doesn't work, then it could be your RAM. Take out one of the 512mb modules and test exiting the game, does it crash? If not, try the other one. Does it then?
Some games by the way do use mroe memory when exiting than others.
This is a sure way of knowing what the problem is. i hope this helps