make certain that you dont have shared video taking away from your RAM...
As for the brand, I couldnt get a GEFORCE to work with my machine because i have other Nvidia controllers built in to my AMD processor/ motherboard etc. Had to settle for an ATI RADEON with 512 RAM and I also upgraded my Computer's RAM. Im not entirely disappointed with the ATI card, getting around 65fps for ~$100 nearly a year ago wasn't too bad.
hmm... maybe time for me to upgrade again...
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