Ok, I just checking it wasn't a quad which in that case your PSU would have not been powerful enough... Are all your other drivers up to date? Things like chipset ect? Plus do you run the 'Dual-core optimizer' driver for AMDs? You can get it here:
AMD Athlon™ 64 X2 Dual Core Processor Utilities and Updates
It's in the middle of the web page. I know your running an opteron but I'd try it non the less. I run it and it does make a difference in games..

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AMD X2 BLACK EDITION 3.2GHz SAMURAI COOLER::GA-M51 MB-HEATPIPE CHIPSET COOLER::3GB XMS2 PC6400 RAM::GEFORCE 8800 GTS 320MB 575/900MHz::160GB BARRACUDA RAID 0::SOUNDBLASTER AUDIGY::SAMSUNG WRITEMASTER DVD-RW/PIONEER DVD::HIPER MODULAR 530W PSU::THERMALTAKE ARMOUR Jr CASE::RAZER COPPERHEAD MOUSE::VISTA HOME PREMIUM SP1