How many watts do I need in my power supply for my setup?

I would recomend at least 600 Watts, but you should go for 850 Watts so you have some extra power to work with if you want to upgrade anything.

How do you overclock a PSU.! Oh ok, must be a typo for CPU.. Your video card is fine till you don't list your game titles you intent on playing and the settings you wish to play on.. I'd recommend you on getting a quad core.. The 955 BE is a great deal to miss.. Being from the black edition family, you can easily overclock it by increasing the multiplier and core voltage.. For your current listing and even considering the 955 BE and overclocking, a good 550 watt unit will suffice.. For that I'll recommend the corsair vx 550W.. Although personally, i like to be very sure while buying a PSU since its one of the most important and integral part of a build.. So i'd have personally gone for a seasonic x-650.. The full modular design takes care of the cable management and its 80+ gold certification says enough for its efficiency.. Reviews around will show you its excellency with voltage stability etc..etc..etc.. Yeah 650W will be overkill for your current rig and pricing is slightly high but it takes care of most of your future upgrades and more importantly gives you peace of mind..

I know how good the 955 is but i only have about $650 to spend. If you can come up with a way to get a 955 BE with that much money, feel free  

How about this?
http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...

I dont think i can do the 955, but i might be able to pull off the 940.

http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...

My point is on getting a quad core so go ahead for anything that fits in your price bracket.. The 940 BE is an equally good choice..

Ok 940 BE it is.

a high quality 550w should do
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

however, i recommend this:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you are thinking about doing cf, the ANTEC TRUEPOWER NEW 550W (by Seasonic) is a terrific PSU for only 80$ at newegg. This PSU presents a combined 12V rating of 45A (540W), which is divided up into four 20A +12V rails (Over Current protected) and one 6-pin and another (6+2)-Pin PCI-e connectors.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...