need help with new build

I have built a new gaming pc and am having problems with it freezing during games (call of duty 4) here is my system info:

amd athlon x2 6400
asus crosshair mobo
4 (2x2gb) gb geil evo one ddr800 ram and 2gb (2x1gb) corsair xms2 ddr800 ram 6gb total
2x 8600gt
150gb western digital raptor x
BFG 800 watt PSU
asus silent square evo cpu cooler

I have also installed vista ultimate 64 bit version.

I have tried multiple operating systems including xp home, vista 32 bit and 64 bit and none fix the problem.

I have tried multiple hardware configs including only 2gb ram, 4gb ram, 1 gb ram, different hdd, 1 gpu, 2 gpu.
I originally thought that it was a mobo issue and rma'ed the mobo. I have also rma'ed the PSU and the issue continues. The cpu is not overheating it runs at about 33-36c idle and 40-43 load. I have ran memtest and have no errors. I am thinking that it is the PSU not providing enough amps on the 12v rail. So I have ordered a silverstone op1000 PSU with a single 12v rail which I hope will help. The only other issue that I could imagine that it would be is that the vid cards are overheating but they dont seem to be all that hot.

Most times the comp freezes and requires a hard restart before I can even fully load call of duty 4 and always freezes before 30 sec of game play. Any help is appreciated I have done all that I can think of and I hope the silverstone psu with single 12v rail will fix it. Also I was looking at my mobo book and it said that it recommended at least a 600w psu so maybe with that much ram and 2 vid cards and 6 fans that it gets overworked under a load. Let me know what you think.

Thanks in advance.
Jason

I have the current drivers for every piece of hardware in this thing. I assume that it must be the psu b/c I only have issues under a large load. I hope the PSU fixes the problem.