Well I bought exactly that cm5570-ap003, originally bought the ap002 which had a wireless card and no monitor. It had a power surge problem and got a refund and then got the ap003 but sacrificed the wireless card.
I put in a EVGA GTX 260 216 http://www.evga.com/products/moreInfo.asp?pn=896-P3-1255-AR&family=GeForce%20200%20Series%20Family
and a 650 watt PSU from Ultra, when I bought it it was only 49 buckshttp://www.compusa.com/applications/SearchTools/item-details.asp?EdpNo=3276573&CatId=106
everything runs beautifully, and I put in two system fans.
The GTX 260 needs two pci E connections and that PSU qualifies
I researched graphics cards and opted for nvidia, but I did consider the ATIs for he features, I recomend you consider what you are going to use it for. Ultra high resolution max settings direct X 10 will need more power, search for best price and what you really need.