Help upgrading my PC please

[Kokoneh]

I have a Dell Inspiron 531S and I would like for it to able to play Starcraft 2 at least at medium.

Parts:
32 bit
AMD Sempron LE-1250 2.2GHz
4GB RAM
nVIDIA GeForce 6150SE nForce 430
120W Power Supply

I'm planning on using a nVidia GeForce 9600GT Sonic and was hoping to center everything else around it, but I have little to no idea on computer parts. If you guys could recommend a power supply, processor, or anything else that would go well with it please advise! I'm also hoping to spend the least amount possible (because the entire point of this was to avoid spending the money for a new computer). Thanks!

 

[MindoverMaster]

What the... You're running that system on a 120W PSU? Before you upgrade, you need a better PSU.

If you have 4GB of RAM, why aren't you on a x64 OS? You can't use the full potential of the 4GB RAM plus the GFX RAM.

What about your HDDs?

Your heatsink the stock AMD one?