AMD Athlon XP 2800
ASUS A7n8x-X nForce2 MOBO
512 MB PC3200
Radeon 9800 Pro 128 (using Catalyst 4.10)
200GB Maxtor IDE HD 7200RPM
80GB (Backup) Western Digital IDE HD 7200RPM
350W Sparkle PSU
I tried the driver update to Catalyst 5.5. No improvement.
Rolled back to 4.11. Worked for half a day, then broke again.
Lowered resolution of game from 1280x1024 to 1024x768. No improvement.
Updated my nForce drivers to most current. Now none of games worked, but at 2D applications were fine.
Replaced PSU with an Enermax 420W PSU with dual 12V rails. Gave the guts of my machine a thorough dusting. No improvement, though machine got a little cooler and quieter

Ran the Driver Cleaner app and reinstalled with OMEGA 5.4 Catalyst and most current nForce drivers. No improvement, no game working.
Did a complete reinstall of Windows XP. Updated security patches, installed Antivirus program, installed (IMPORTANT I THINK) OMEGA 5.4 Catalyst, OLD nForce drivers (forgot which, the ones that came with mobo). Installed GW. Been running strong ever since.
Now, here's some helpful info, since I realize that any one of those final changes could have done it. I received an email from ATI today that stated that the fix to my problem (if I was using CAT 5.5) was to apply the CAT 5.6 patch that is coming on June 17. The wording of the email alluded to the idea that the most current drivers were causing problems on a lot of machines and CAT 5.6 is their response to it.
However, ArenaNet also released patches today, which is when I completed my reinstall, and listed in their updates is "rare crashing problems fixed".
So, could have been drivers, could have been XP needing to be cleaned up, could have been ArenaNet. I know this isn't a conclusive answer, but I am up and running, haven't crashed yet (4 hours running) and at least I can play again.
FYI