What driver version are you running ?? - the newer Nvidia and ATI frivers have some issues with AGP video cards (and then combine that with the strange tweaking Nvidia tried to get away with on the FX series cards (they tweaked the way the shaders were implemented to get better benchmark results) and you wind up with issues !!
Try using an older version of the Nvidia drivers instead of new ones Here is a link to the older 93.71 version that might work -- ( Linkie
Download them and then boot into safe mode - remove the current drivers - reboot again in safe mode and install these - then reboot and see if they work !