Johnnydoe and Severus, your problems are most likely different even tho you have similar 'symptoms' (the crash). Please read the sticky post If you have a problem, PLEASE read this first!
and then post the information either here or a new thread.
Both of you, try both available AGP drivers, AGPgart and NvAGP. If AGPgart is compiled as a module in your kernel then you can control which of these is active by using the option below in the Device section of your X config:
Option "NvAGP" "n" # where n is 1 for NvAGP and 2 for AGPgart
Severus, try using the non-smp kernel first.