You get get any graphics card with it but you will be CPU limited.
Also, you will be CPU limited in games that use more than 2 CPU cores no matter what video card.
More information about your situation would be useful.
But in general, I guess you should be looking around the radeon 4850/4770 (90% performance of 4850 at fraction of cost)/4870/5750/5770 or Nvidia GTS250/GTX260/GTS450 range in order to avoid going past the point of greater returns due to a CPU limitation.
I couldn't help notice you didn't include a pricerange, so I assume you have an unlimited budget. Which makes me ask, especially with that power supply, why don't you buy a new CPU along with your new GPU so you can get more?
Games are certainly GPU dependent but that by no way means they do not use other system resources, especially the CPU. The CPU MUST be able to keep up the exchange of information as fast as the GPU can use it, otherwise the GPU's performance will suffer.
Most multi-core games, like dragon age or FSX are heavily CPU dependant and therefore need the power that multi-core will allow.
Based on the games you mentioned:
MW1 - can only use up to 2 cores
MW2 - can only use up to 3 cores
BFBC2 - can use at least 4 cores
GTA4 - can use at least 4 cores
UT 2003 - I am unsure. likely only 2
Street fighter IV - again I am unsure.
what do you think about phenom ii x2 555
Any game that can only utilize 2 CPU cores or less, will run more than fine on your Athlon IIx2
or athlon ii x4 640.... i won't unlock the 4th core
uhhhh... the Athlon IIx4 640 already has 4 cores, hence the x4.
Anyway, it's a great CPU and will only struggle when cache comes in the way of performance, or lack thereof. Gaming is one of those applications. But with a high clockspeed it can make up a lot of ground.
.i changed to a corshair 850hx
That is more than enough to power a phenom IIx6 and crossfire radeon 5870s.
Ok so now my suggestions, which will come after you tell us how much money you originally intended to spend on the graphics card?