FWIW, I put the Sapphire 4650 into my 530s, without upgrading the power supply, and it runs very well.
I'm running Vista 64-bit, 4GB RAM, and two HD's in RAID1, a fast 4GB thumbdrive for ReadyBoost, along with the 4650, and I haven't had any issues with the power.
In playing AH, the frame rate is usually bouncing between 59 and 60 at 1280x1024, only slowing down in large furballs. It ran higher res fine too, but I had trouble making out the details since things were so small.
It's this card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102829The card also overclocks pretty well without getting too hot, so that's a big plus since the 530s case has mediocre airflow.
mir