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1) try unchecking the "Use Desktop Resolution' box in your game settings.FPS will shoot up guranateed.
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I tried this earlier but instead of boosting fps i got lower fps.
My System:
MacMini
2.26 GHz Core 2 Duo
2 GB 1066MHz DDR3
Nvidia Geforce 9400 256MB
and running WinXP on my Bootcamp Patition