Well, I give up. After many days lost to this error and after many false hopes dashed I've thrown in the towel. I've pulled the GeForce card and gone back to the RIVA TNT. The RIVA works flawlessly with the new drivers, I might add. Very nice...
For the record, these are things that didn't work for me either singly or in any imaginable combinations:
1. Selectively disabling software that seemed to hang.
2. Changing the value of NvAGP to anything at all
3. Changing the value of NVreg_RegAGPRate to any reasonable number
4. Reseating the card multiple times
5. Changing to a power supply with 28A on the 3.3V rail.
6. Altering any setting in the BIOS that has to do with AGP or video or memory or whatever
BTW, I was getting glxgears to turn at over 350 fps at AGP 2x with this card before it would lock up! The RIVA gives me about 160.
Google searches yield literally thousands of people who are experiencing this error under various configurations so I would imagine it will become more of a concern to the community at large as time goes on.
Well, thanks for your help, brblueser. I really appreciate your help and concern...