No it's not pre-built, I will be willing to go down to a 500W PSU. I just was not sure on the Watts needed, PSU's always confuse me. Also yes there is other motherboards, What I was planning on doing, which is why I had the 650W PSU, was just to get a new motherboard, and 1 more HD 5850 down the road, but I guess it would be cheaper to get a motherboard now with 2 PCI-e X16 slots, and upgrade the PSU later.
Edit: Would this be a good motherboard?http://www.bestbuy.com/site/Asus+-+ATX+Motherboard+2000/1600/1333/1066MHz+(Socket+LGA+1156)/9724535.p?id=1218159865250&skuId=9724535
With this PSU: http://www.bestbuy.com/site/Thermaltake+-+500W+TR2+ATX+Power+Supply/9827259.p?id=1218179698118&skuId=9827259
And just another set of the memory I already have down.