Yeah jsc basically said it. I really depends what else you are running, I mean if you have that cpu using onboard graphics 1 optical drive and one hard drive you could run a 300 watt psu all day, but if you are using a discrete graphics card a couple of hard drives and optical drives, overclocking, SLi, CFx, etc. you could need anything from 500w to 1000w.
So to answer your question... Tell us what else you want to run in the system.