Go with a P45 board, Gigabyte has some $100 boards that are good. DDR2 ram is very cheap now a days so two sticks of 2Gig memory won't cost you very much. A 400-500W PSU is all you'll really need since you only do light gaming. You could probably get away with a 350W PSU depending on the GPU you choose. Go with either a 4670 or a 4850. The 4670 probably being a better choice for you since you can get it below $100 for a good card that if you want later can be crossfired.
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