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which most manufacturers would call 330W. Your choice of video card is mostly limited by the speed of your computer, not the PSU rating. That system uses a S423 Willamette P4. You should have no problem installing a Radeon 9800 Pro or 6600GT in that system. Even a 6800 or x800 would work, but it's overkill.
Powerleap sells an adapter for that system for around $50: http://www.powerleap.com/PL-P4N.jsp so you can put up to a P4 2.8GHz/400MHz FSB Northwood in it. (ebay has great prices on CPUs... use the coupon code CELEBRATE on paypal to save 10%.) It's up to you to decide if adding more than a video card upgrade to that old system is worth it.