The problem is that your card is a 5200. Haha.
OK seriously... this sounds like a real beyotch. Grasping for straws here, but I might try:
1- Try the 5200 in another machine to see if it works OK. It might be a bad card.
2- With the 4200 in the machine, use detonator destroyer to remove all nvidia drivers. Shut her down and then try rebooting with the 5200. If it's a driver issue this might take care of it.
If that doesn't work, I don't know what to say. I hope you're running a decent power supply (at least 350 watts name brand or 400 watts generic) with this rig...
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Radeon 9500 (modded to PRO w/8 pixel pipelines)
AMD AthlonXP 2000+
3dMark03: 3529