I don't want to depress you, but you have a problem. I know for a fact that your current PC is not made for heavy gaming, in other words it is far too outdated; even if you manage to upgrade your PSU and get a 4670/4650, your CPU @ 2.2Ghz will bottleneck your graphics card and you will lose a significant amount of performance.
If your planning to play games like crysis or sims 3 on even medium settings, I suggest you buy or build a new PC.
Just so you have a idea; your current system is single core CPU @ 2.2Ghz and 512 DDR ram. To even play the games you mentioned, you will need at least a duel core @ 2.2Ghz or higher CPU with 1.5GB or more of Ram depending on your operating system with a 9600GT graphics card and a 400 - 450Watt power supply.