Out with the old, in with the new...

[Crandaeolon]

Check out the deals you can get, a C2D E8400 would be a better choice for current games. It has more performance per core (and 90% of games still use only two cores at most) and overclocks extremely well. Still, go with the Phenom if you can't find a similarly priced E8400+mobo.

A 700-800W PSU is overkill. 500W should be enough, even accounting for years of capacitor aging, unless you have lots of peripherals. In any case 600W is pretty much the highest sane option for that system. Here's a handy calculator: http://www.thermaltake.outervision.com/Power