GeForce 2 Pro, XP Pro, OpenGL Lockup/Video Garble

In games like Quake III: Arena, MOHAA, Tribes 2 and Half-Life (any mod, in OpenGL mode), my computer will randomly lock-up mid-gameplay and the screen will turn to a garbled mess of flickering lines. Ctrl-Alt-Delete sometimes works, but most of the time I have to hard-reset the computer via the tower case button. I have used the 21.83 nVidia reference drivers, 23.11 reference, 23.12 (via Windows Update), 21.83 from Leadtek’s website and the leaked 27.42 nVidia drivers (www.reactorcritical.com). Every version of the drivers has caused the same problem. I have also updated my chipset drivers from Intel to the latest version to no avail, as well as checking for sound card drivers. I have read through Leadtek’s FAQ and all the settings listed that I could change in my BIOS are correct, and I have tried setting my AGP Arpeture to 1, 1/2, and 1/4 of my system RAM. I can NOT modify the AGP speed from 4x in either my BIOS or via the ‘PowerStrip’ utility.

Disabling ‘OpenGL Extensions’ in Quake 3 prevents the lockup from occurring as far as I can tell (it may just delay it) at a severe cost in FPS and image quality (no reflections, etc.) Please help! System specs below:

Intel Pentium 4 @ 1.8 GHz
Gigabyte P4-Titan GA-8ITXE
256MB ECC-RDRAM
Leadtek GeForce 2 Pro w/ 64MB DDR-RAM (AGP 4x)
Creative Labs Sound Blaster Live! Platinum w/ Live!Drive 1
ATI TV-Tuner PCI
D-Link DFE-530TX+ 10/100BaseT
IBM-DPTA-372050 20.0 GB ATA/66 HD
CompactFlash reader on LPT1 (pass-through to Canon BJC-5000)
Brother HL-1250 Laser Printer on USB
Sony DVD-ROM DDU220E
Yamaha CRW8824E
Microsoft Windows XP Professional (all Windows Updates installed)