Unfortunately I think that is over my PSU limitations. As I look more into it, I may be asking for something non-existent.
I don't know ... if you're going by the manufacturer's recommended specs, they ALWAYS greatly exaggerate the wattage you'll need to run a card. Fact is, they don't know what the rest of your system specs are, so they assume the worst power-hogging components they can think of. It's a cover-their-ass kind of thing.
At any rate, I have a 4650 running on a machine with a 300W power supply, and have heard of countless others getting it to work on 300W or even 275W. On 250W I don't know for sure, but there's a good chance it will. If you're worried about it, you could always pick up a cheapo 300-400W power supply for like ... $15-$20.http://www.newegg.com/Product/Product.aspx?Item=N82E16817170015
Now, people always say it's important to get a PSU from a reputable brand because there really is a difference (and there is) ... but in a case like yours, where there's such low wattage involved and the system is so old to begin with, you really have nothing to lose, so I'd say go for whatever won't break your wallet.