Decent Rig with FPS Slowdown in a lot of FPS games.

This is my rig:

AMD 64 3800
MSI RX800 TD 256 version
1.5k ram (512X3 333mhz)
nForce4 ECS 40 A939 mobo

I Just upgraded to this system, and everytime I try to run a game, (CS:Source and, UT2004 mostly, both games on 1024 resolution, and Normal settings) I notice that whenever I turn corners my FPS will drop, or it will become incredible choppy (70fps to 30-40fps). I have tried installing several different version of Catalyst drivers (6.9, 6.7, 5.12, 5.7) and I still get the same result. Also re-installed windows a couple of times, and I think i have come to a conclusion, that the problem is one of my hardware. Anyone have an Idea, what could possibly be causing this?.

I Also tested my ram, and they seemed fine, even left one at a time, and I was still getting the same result.

Also ran a couple of 3dmark05 and 3dmark06 benchmarks.
3dMark05 = 3950 - 3990 (could never break 4k)
3dmark06 = 940 and 980.

If anyone knows what's wrong with my computer, please tell me I have ran out of ideas on how to fix this.
Thanks in advance.

 

How many watts is your PSU?
Have you got vsync turned off?

 

PSU is 450Watts.
Vsync is off.

 

Update:

Borrowed my friend's 7900GT, and i'm still getting the same results (Choppy in corners and wide areas).