I would hold off until you get a better PC. its now standard for gaming rigs to have a a quad core CPU and 8 gigs of DDR3 ram to run most games decently. I also agree that you should go with Nvidia. They have much better drivers which is really important. I don't know what your budget is, but I would say you should get something between a GTX660Ti (which is pre-overclocked) and GTX 680. Those are more than sufficient. The higher cards, like the 690 and the new Titan are $1,000. They are worth the money.....but unless you have that much cash to burn, you dont need it. The other cards I mentioned will run you between $400-$600.
Ram is super cheap now and a 3rd gen quad core cpu is about $300-$400. So take from that what you will. It also helps if you have a decent motherboard to for compatibility sakes and performance. They are not AS important but still needs to be considered for a proper rig. I would also suggest a Power Supply with 1000w. Corsair is the best make for that. For Ram, look for Patriot or Mushkin. Hope all this helps.
Edited by DragonChi, 10 March 2013 - 03:06 PM.