Depends on what you are doing. For gaming I would just get a Phenom II x4 955BE or 965BE and get the nvidia 460 with 1GB RAM. Its very rare to find a game that uses even 4 cores, much less 6. If you are going to do alot of video encoding or other massive mathematical applications them maybe the 6 core would make sense.
Look at the power supplies forum and check out the info in the sticky at the top. Poor power supplies can make your system do flaky things like lock up. Bad PSUs can damage motherboards, RAM and video cards. Make sure you get a good quality PSU and avoid these problems.