For the motherboard I suggest the ASUS M4A77TD.http://www.newegg.com/Product/Product.aspx?Item=N82E16813131603
AMD Athlon II X3 445 Rana 3.1GHz is a great CPU and with any luck the ASUS will unlock the 4th core. This combo gets you a 5770 for not much more than a 5670 would cost.http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.500403
I got you an Antec case with 430 watt PSU with a dvd burner combo deal. This is an amazing deal and the BP430 Watt is the same my son uses for his XFX5770.http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.492952
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 is very good memory.http://www.newegg.com/Product/Product.aspx?Item=N82E16820231277
Currently the best deal on HD's is a WD 500GB blue for $40. Dont forget the $15 promo code.http://www.newegg.com/Product/Product.aspx?Item=N82E16822136073
Total will be $500.90 plus shipping. There are a good amount of rebates on these deals also.