Maybe your problem is that your games' FPS are limited by the monitors refresh rate (RR)! Therefore you gotta set it higher and your FPS goes straight up!
Sounds easy ain't it? But it isn't in XP!
XP limits the RR to 60 Hz! If you have a ATI Radeon Graphics Card its easy to set that limit higher!
Just go to display\settings\extended\display and click on your monitor!
There you should see the monitor's properties.
Just set the maximum RR higher (maybe the resolution as well) and there you go !
I hope I helped you out with that!