I've got working environment and had also strange errors with X-server and GeForce4 MX 8x AGP.
Does your system boot straight to kde or gnome?
Try booting to text-based mode and install nvidia drivers.
They can be found from here:
On thing with nvidia drivers is that it is build "with" kernel. If you recompile kernel you'll have to install those drivers again, but if you won't recompile kernel, just install that package.