Re: Upgrading Dell Dimension C521
my guess is that it would need a bios flash to take a new cpu and more than 1 gb of ram per slot. or maybe not since it is a prefab.
to be on the safe side, i would just grab 2 or 3 1 Gb sticks.
it sounds like you have a gpu installed.
click start, control panel, system, hardware tab, device button. open up the display adapters and tell me what is listed there. you can probably pick up some more performance with a gpu upgrade than the cpu upgrade for gaming.
Intel Core i5-2500K
ASUS P8Z68-V LE LGA 1155 Intel Z68
1Tb Samsung Spinpoint F3
1Tb WD Caviar Green
2Tb WD Caviar Green
8gb DDR3 Corsair Vengeance 1600
Sapphire Radeon 6870