Maximizing FPS on my new computer

hey all, myself and a friend have recently put together a pc. Im using it to 5 box. From most of what i read on here i should be able to get good frame rates with what im using but there fairly average (25ish at times) at most depending on what area im in. Shattrah is still a nightmare :-p Im mainly wondering what tricks you can use to up your FPS.

My current system specs are
Intel Quad Core 2.83ghz processor
Asus Engtx 260 graphics card
Asus P5N-D motherboard
Kingston 4GB (upgrading shortly to 8gb its being shipped) Ram DDR2
Aerocool EN53099 750watt power supply
2-22" Westinghouse Flat Panel LCD monitors
Western Digital 500GB Caviar HHD

Im running Windows XP64, i use keyclone, and i set it up so 4 windows are on one screen and 1 is on my other screen. if this helps at all <_<