I have seen this problem described before but none of the solutions that I have found seem to have worked. I am using Gentoo Linux + The latest NVidia drivers xorg(tried the older 50.00x ones too, same problem). I can fire up XOrg/Gnome just fine however after a bit of using it, the computer locks up. The mouse still moves however the windows all freeze, and stop responding and ctrl-alt-f1 and ctrl-alt-backspace do nothing.

Rivafb is not compiled into the kernel. Kernel is using vesa fb. Turned off DRI, didn't fix it. Turned off agpgart and recompiled kernel without agpgart, didn't fix it. Re-emerged Xorg, didn't fix it.

I can always reproduce this by opening up Mozilla and pointing it to a site like fthis one. It usually locks up in the middle of loading the forums. I also got it to lock up just using aann x term.
Because I am stuck using links at the moment I've uploaded the latest Xorg log and xorg.conf to (add http :// in front of it) 66.57.87.26/logs

dead link.... but, have you changed the Xorg.conf file to use the new nvidia driver? Anything that says nv should be changed to nvidia.

Try turning off apic in your grub.conf kernel parameter:

kernel /gds-2.6.8-r2 ro root=/dev/hda3 noapic video=vesafb:ywrap,pmipal,1280x1024-32@85 splash=silent,theme:emergence

This was an issue with nforce boards for a while. I thought it was fixed. What kernel sources are you using?

I'm using a VIA chipset, though I wish I had an NForce. I managed to get it fixed after a lot of tweaking by setting my card from AGP 4x to AGP 2x in the BIOS setup.