I have had a very similar experience to most of you here. I also have an Athlon XP 1800+ CPU, and on the VIA KT266 system. I have tried both Red Hat 9.0 andMandrake 9.1 on this system, and neither was stable. The symptoms are familiar to all, I am sure: most repeatably, whenever I'd launch a web browser, the system would do a fatal lockup after connecting to an external web site.
I did a complete blow-away, repartition and virgin install of Red Hat 9 yeterday with the stock kernel and successfully installed the nvidia drivers. Dmesg and the logs show no anomalies, except one:
There seems to be some conflict with the VIA's on board IDE controller causing drive timeouts during initialization.
Following the suggestion of several people, I went into the BIOS and stepped down from 4x AGP to 2X. For the first time, I can surf the web and download.
I'm not blaming nVidia here, but I do suspect there's a latent BIOS conflict in the memory addresses reservered by the VIA on board IDE controller and the memory address range used nVidia with the GeForce FX series.
I'll try getting the latest BIOS upgrade, which is about US$39 to see if that corrects the problem.