OP, do you need to buy the OS as well? Is so, that will have an enormous impact on what kind of hardware you can afford to get with a $650 budget. If the $650 is hardware-only, my recommendation would be an Athlon II X4 and HD 5770 set-up. Throw in a quality sub-$75 PSU at 500-600 watts (such as this Antec - http://www.newegg.com/Product/Product.aspx?Item=N82E16817371030), get an affordable but full-featured mobo (such as this - http://www.newegg.com/Product/Product.aspx?Item=N82E16813157198), one of Cooler Master's many attractive, sturdy, $50 mid-tower cases (personally, I favor the Centurion 5 - http://www.newegg.com/Product/Product.aspx?Item=N82E16811119068&cm_re=cooler_master_centurion_5-_-11-119-068-_-Product), a relatively cheap 4GB kit of DDR3, a $50 500GB HDD (there are a couple good ones out there at that price) and an optical for less than $30... That'd be a very solid and well-balanced rig.