find the bottle neck

[N0de]

I just got UT3 and its nice but I figured my system would run it a bit better than it does. Im getting an avrage FPS in the 20s with a lot of things turned down or off. Also there are horrid spikes, upto 60fps and down to 11fps. Its not stable at all.

Specs:
X1900XTX stock clock running 67*C idle 77*C max loaded
P4 3.4ghz running in the high 50*C range or low 60*c range under load
2gb dual channel Corsair XMS DDR2 4-4-4-12
Asus P5AD2-premium mobo
SATA HDDs
350watt PSU

Im not too sure whats holding it up or if anything should be but my frames seem way low.

Thanks