well, I must stand corrected. I rebuilt a machine with my old Neo2, A64 3000+, and the BFG 6800GT AGP, and after I flashed the mainboard BIOS to the most recent, the card was reasonably stable. Before, it would routinely crash in any 3D app within 30-90 seconds, hanging the entire machine. After the rebuild, it would complete 3DMark05. But after a couple of hours of looping 3DM05, I get the nv4_disp infinite loop hang.
I put the card back in my A8V r1.02 machine, and it also hung with the nv4_disp infinite loop problem, but after 6 hours instead of two.
I'm not sure what I'll take away from this, could be I have a bum card, I'll be talking to BFG.
EDIT: Just an update, I ended up RMA'ing the card to BFG, and got a brand new one in return. I popped the card in the system (Neo2) after removing all old video drivers, installed the latest nvidia drivers, and the system seized after about 90 seconds in 3DM05.
I ended up selling the card and getting an ATI X800XL, which performs flawlessly in the same system.
So in conclusion, it's my finding that there is in fact a readily demonstratable, albeit not universal, incompatibility with the Neo2 and the 6800GT. There's too much discussion of it online for it to be entirely without foundation, and my own testing, however limited, bears this out.