If you are looking for a MOBO (mother board) get a Z68 or better. With your PSU's (power supply) get Corsair, Antec, Seasonic, and XFX. These are in the top line of PSU's.
Those are the PSU's you should be looking for. Thers are a lot of junky one's out there so be very careful when looking for the righ one. Other than that you have a nice set up going.
Just do your self a favor and get either the GTX 560 Ti Hwak or the HD 6950 to start. It might put you over the 1000 dollar mark with these up grades. But if you want a rig that will game as good as the Xbox and better then you have to. Good luck