Gaming computer recomendations?

Im considering getting a new computer to replace my three year old frankenstein machine. Im pretty sure the specs are(not using that computer atm), 2.2 GHZ amd single core processor, 1 gig ddr ram, 160 Gb 7200rpm hard drive, mobo capable of having an amd X2 processor if its the right size and i think 4 Gb ram, and an Nvidia GeForce 6200 that i managed to unlock extra pixle pipelines for and overclocked the hell out of it. I think ive got around $1000 to spend on a new computer. I want something good for gaming, ex. Oblivion, Crysis, but i dont expect it to be able to handle Crysis on very high settings, obviously. Im also not afraid to work with the parts and build it to reduce cost, mind you, im no expert. So what would be best, upgrade my current machine, or start from scratch?