I have Fedora core 1 as well, and a GeForce Ti 4200 - and get exactly the same problem. If it is the same problem, it seems to be caused the first time X is started, as if you boot to a console, login, then run startx from there, the first time you run it, it will die, but if you run it a second time it runs fine.
I also get about 4 frames per second on glxgears, do you have slow GL or is it an unrelated problem? I also noticed that when I run xdpyinfo, NVIDIA-GLX is missing, yet GLX and NV-GLX are both there, although according to the 'installed files' section in the README supplied with the drivers, all my symlinks are there.
I've attached my X log, any help would be most appreciated.
"Thought.dll caused an invalid instruction in module brain.exe and will be terminated"