Manually editing the registry is often frought with danger, perhaps try running System Restore and restore to an earlier date when you know the PC was running fine. When it shuts down after applying the change you could then uninstall the old gfx drivers, then install the latest GeForce gfx card drivers (see below).
Ideally you'd want 350W but since your PSU is Antec (reportedly the best) you should be totally fine there.
Even though you uninstalled you old drivers and did everything right, there is still a chance that your old drivers have left remnants in the Win\System folder, INF folder and registry. The only sure way of get rid of this stuff is to do a completely new install of Windows, but you shouldn't need to resort to that!
2 things which really jump out at me are your mobo (VIA KT133, very old) and SB Live (big probs with VIA chipsets). SB Live cards hog both the PCI bus and CPU, it is the former that is weak on the VIA chipsets and this exaserbates the problem, however a patch (VIA PCI Latency Patch) is widely available and is ALWAYS worth installing. Another good step is to get the latest WinXP (Win2000 will do) drivers for ALL of your hw, including BIOS. Be sure to check both the chipset (eg VIA & nVidia) as well as manu (eg Aopen & Visiontek) for the latest non-beta drivers, the manu website should list compatibility info and any tweaks or quirks.
I strongly expect it is your mobo, KT133 came out at the birth of the SktA mobos and as such could be causing compat probs. I have heard that VIA mobos and nVidia hw are the most prone to the infinite loop bug. In any case try looking at your BIOS settings, disable 'PCI Master Read Cache', that is often the culprit. Other measures are to note the settings and try altering anything regarding the AGP bus, sometimes changing 4x to 1x can help, at least until you find the route cause. In any case the latest mobo BIOS is always good to have, esp with new hw.