XP SP3 system locking up

A few days ago I uninstalled several anti-malware programs in an effort to speed up my XP SP3 system. I used Revo Uninstaller to make sure they did not leave any remnants behind, but I am afraid I may have corrupted the registry by deleting too much.

The computer suddenly started locking up with no warning, no BSOD, and no entries on the event viewer. Everything on the screen just freezes after 10-30 minutes, with no mouse or keyboard input appearing. Only the power and reset buttons on the case do anything.

At first it seemed to do it only when the default XP screensaver activated, so I turned the screensaver off. Then I thought maybe it was a problem with IE8, since my wife said it crashed when she was listening to AOL radio. I installed the latest version of Firefox, but still no dice. I tried several generations of System Restore points, but none of them were able to save me.

I finally backed everything up and did a repair install from my XP SP2 disk. I had to reinstall my audio drivers from the motherboard CD, but networking, graphics, etc. all worked. I installed XP3 and all the latest security updates, as well as the newest nvidia graphics driver. While trying to install IE8, i don't think the installation process ever completed correctly. When i tried running Microsoft Update or launching IE, it gave me a message about some libraries not found. Firefox said I didn't have a network. While reinstalling the network drivers from the motherboard CD, the system locked up again. Now every time try to restart it, Windows doesn't start up at all, and I get the message "Windows could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM"

System specs:

Athlon X2 4600+
DFI LANParty UT nF4 Ultra-D (BIOS 03/29/2006)
2 x 1gb OCZ EL Platinum PC3200 (stock 2-3-2-5)
stock cooling
MSI 8800GT GPU
OCZ 550w modular PSU
onboard sound (Realtek)
640gb WD SE16 HDD
NEC PATA DVD-RW