I'd recommend upgrading your PSU. HP uses generally crappy PSUs and a great PSU for such a machine as yours could be bought for under $50. The other $100 or so could be spent on a Radeon 7750 or a discounted Radeon 7770. Either card should do well for gaming, but the 7770 is significantly faster for not much more money. With MIR, there is a 430w Corsair PSU (assuming that the MIR is still going, I'll have to check) at Newegg for $25 and you could easily get a Radeon 7770 with the left over money if you want to and if not, a 7750 is still considerable.