Moderate Gaming. Not ground breaking - I save that for my ps3 - but Total War, Age Of Empires, etc.
As is the case with my hard drive, I'm waiting to see a) how much money i have left over. and b) if I get more work (which = more money )
If I can, a new graphics is in consideration.
For a cheap upgrade, a HD5670 is relatively inexpensive and will offer vastly improved performance.
As to the PSU, I'm not sure what's available to you. Essentially, a quality modern PSU has full range active PFC (no little voltage switch) and 80+ certification. Antec, Seasonic, Corsair, and Enermax are among the better brands. A 380W Antec Earthwatts is a solid choice for a PC like yours. You could upgrade to a HD5750 or HD5770 with that.