Okay lets do this

[LiNuX]

Well, is the 9100gt an addon card? And perhaps asking your brother might help.

Also download speedfan or a similar program and look at he temperatures for your hardware. I used to lag in most games after playing for 20-30 minutes because the graphics card kept overheating. For several months I thought another program was interfering or something but it turned out the GPU was overheating.