Need Help Bad FPS

My brother has a Dell XPS 400 intel Viiv with 2 gigs of ram, 2.8 ghz dual core( not Core Duo) pentium

with a Geforce 8800 GTS 320mb vid card.

 

We got this card from Dell, but just like the X1950 ATI card we got before it performs very poorly when he plays certain games. Namely Guild Wars. While out exploring or questing ingame, if he doenst move. he gets upto or over 60fps but when he moves it drops to below 13 or futher down, and has horrible game play. Gets really jerky and choppy. Stock 375W PSU. Also he is running on a wireless connection and has excellent strength, at 54Mbs.

 

I my self have a similar set up.

 XPS 400 2.8 Ghz Dual Core( Not Core Duo, Oh How i Wish) with 3 gigs of ram, a Asus En7950GT card 512mb , and have no frame rate drops below 30 when i play, maybe if things get really harry it will drop below 15 , but i dont have the utter chop he does and my card is not as good as his. Also i have and extra 275 watt psu from thermaltake. But i have seen no performance difference, I just wanted it to have its own PSU. Her does not have a seperate PSU but i dont think thas the problem.

 

Is there something I'm missing here.

Please help if you can...Thanks in advance, if you need anymore info let me know.

Also i have the lastest drivers installed and lastest Bios for his comp also and chipsets.

 

Also we both have XP Media Center Edition with SP2