Sorry, I've been using Via chipsets for too long.
If you don't have Atigart.exe then don't worry about.
Try downloading a utility called Geforce Tweak from <A HREF="http://www.guru3d.com" target="_new">http://www.guru3d.com</A> and use it to manually set AGP to 1X. If this works then it is likely that AGP 2X is just not stable on your system. If it doesn't work (meaning you can switch to 1X but you still have the same problem) then uninstall the AGP driver and start over again.
As someone else mentioned, if you have AGP v1.0 then AGP 2x may be unstable or it may not work at all. Many motherboards had problems with this.