random system freezes

i've been getting random system freezes for a while now. this problem seemed to come out of nowhere. the freezes most often occur during game play (usually newer games such as Doom3, HL2, UT2004). when i first began having the problem, i suspected my sound blaster audigy card because, when it would lock up, i got what was known as the "squeal of death." lately, however, the freezes have been squeal-less. i've experimented with the sound card by performing driver cleansweeps (as directed by creative's support staff), BIOS settings changes, and putting it in a different computer. i was fairly certain the sound card was the problem because it even caused the other computer to lock up randomly. so, today (after removing the audigy) i formatted and reinstalled windows xp pro with sp2, performed all the necessary windows updates, and installed the correct drivers. once the system was fully functional, i only put a few additional things on it. winace, firefox, and half-life 2. to test for freezes, i played hl2. after about 20 minutes of play, it froze. i just restarted and played again for half an hour without any problems.

i have no idea what's causing my computer to freeze... or when to expect it. it might help you to know that around the time i was getting the squeal of death, i had a different motherboard, cpu, and ram combination. then, i had an Asus A7V333 with 512MB of DDR333 and an Athlon XP2800. now, i have an Asus A7V880 with 1GB of Corsair XMS (running at dual-channel DDR400) and an Athlon XP3200. other than my video card (ATI Radeon 9800 pro 128), there are no other cards installed. i'm using the onboard audio and network adapter. usb mouse and keyboard. sata hard drives. there is sufficient cooling.

i thought maybe one of you guys might have a few tips for me.. or maybe a few things i could try. thanks in advance for any help.