Holy crap! A 1000W PSU??
Phenom 9950 140W
And that's without the HDD and disc drives :P
But we aren't there yet :-o Enter 80% efficiency >.<
650W * 0,8 = 520W PSU
1000W * 0,8 = 800W PSU
Also , googling for <"club 3d" + HD4870X2> yields quite a few posts on various forums with people getting bsod on Windows XP with this card... It *could* be that Club3D made a shitty card... ?
Try to make sure it is adequately cooled, maybe it is overheating...