low fps with top of the line system???? please help!

system specs:
intel p4 2.6 800fsb
ABIT IC7-G max III motherboard
2048 mb DDR kingston pc 3200
(2) seagate 160Gig HD 7200rpm
RadeonX800XL 256mb AGP videocard
soundblaster audigy 2 gamer
22" sony trinitron flat screen moniter
logitec 5.1 surround sound speakers @ 500w

when i play certian games like hl2,bf2, and in this case UT 2004 i get very low fps in high action battles. when im just running around i get great fps and on smaller maps i get good fps unless there are a lot of people in the server. ive tryed changeing video settings to 800X600 (i usually run at 1024) and it is still choppy. ive also tryed turning off all backround programs through taskmanager and that dosent work either. I NEED HELP!!! please any comments would be very helpful.

thanks

what else are you running at the same time?

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notihng i stopped all of my backround taska and it didnt help