You will be able to play older games like Half Life 2, Counter Strike, Halo, Oblivion, Battlefield 2, Doom 3, Far Cry 1, Age of Empires, and others from that era at fairly high settings; however, you should not bother trying to get games like assassins creed, far cry 2, and Crysis to run.
If you want to get serious in gaming, i would save for a new system. Or buy a cheap Gateway or Dell (saw a Phenom X4 2.2, 3 gigs of ram, 500 gig hard drive, 780g (i think) for $350 and add a PCI-E video card)