Not much, frankly.
Worst-case load power consumption isn't going to break 350W - I can't find perfectly comparable numbers, but a system with a beefier GPU (GTX260 c216) and CPU (OC'd C2Q QX9770) doesn't hit that level, either. A good quality 450W or 500W PSU should be plenty - less would probably be fine, too, but it can be hard to find good power supplies much below that point, and a little breathing room isn't a bad thing.
EDIT: Bah, ninjas
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