Last week I bought 4 CX430 PSU's on sale for $17 after rebates (430 Watt) to replace several P.O.S Logisys 480 Watt (which have EXTREMELY high failure rates that came with the cases of some older systems. These have been long overdue to be replaced. At the time, I failed to remember that the recommended PSU for a Readeon 4850 was 450 watt. 2 of the systems are running 9800 GT cards (which reccomends a 400 Watt PSU) on the box, so I am positive those 2 are fine. The others run a PowerColor 512 MB Radeon 4850 on an Athlon II X2 245 2.9GHz CPU (no overclocking) and a single hard drive. I know I am riding the margin... but certainly they over-rate PSU requirements on Graphic Cards to have a bit of a safety magin and tolerance for the variations in CPU, motherboard, fans, harddrives and everything else that draws power don't they? You guys think this will be fine?
It needs a minimum of 450 and a 6-pin power connector, but I've seen people run cards on way lower PSU's and it works fine. The only thing that would happen if it wouldnt be able run would be that your computer would boot up and run slow, or when it comes into load you might freeze, or blue screen. But corsair builder series PSU's are pretty high quality and you should be fine.
the total power draw of the computer is rather modest: 189W. A 300W power supply will ensure a 50% reserve of wattage, and there is absolutely no point in purchasing anything better than a 400W PSU for this configuration.
Thankyou EVERYONE for your help and overwhelming confirmation. I had a tough time narrowing down the "best answer", and I just want to let you all know that I appreciate each and every one of you for taking the time to reply and give meaningful input. It looks like the margins for the Power Supply Ratingings are marked up ~50% of what is actually drawn on a typical system from you guys's replies. Is this generally the case with with the listed PSU "minimum" requirements? Or is this a special case? I would think its done because there is a VERY wide range of hardware any user might run in conjunction with a video card, from low end/low power parts to multi-core multi-drive configurations with a board decked out with all RAM slots filled. So the req's on the box gotta factor those extreme cases basically?