Might just be me but i would go with a PSU higher than 500 watt. Just to keep it from working to hard and cover and future upgrades i.e. SLI , more drives, etc...
I hate when i find someones PC is unstable due to a weak PSU.
I was thinking of rather buying the Zalman ZM600 HP. 600W Modular PSU, and I've read good reviews about it too.