Try changing your AGP card properties,i mean,try changing the speed of working of AGP card.Try different values like 1X,2X or 4X.I think it must be 4X currently,so try 2X.Also try out various other options about AGP card.Atlast ,you can give a try to 3DAnalyser,which helps in emulating any display device as high end card and it has got various options.