I'm considering upgrading my GTX 460 with a 660. The one I was looking at has a 450w min requirement and I believe my current PSU is 500W (I'm out of country right now so I can't really check). In the future I plan on upgrading my athlon II x4 640 3.0GHz with something more powerful from Intel when their new stuff comes out.
My question is if my 500w would be enough for the card and maybe an OC on the Athlon?
Not unless it's good branded unit such as antec, corsair, seasonic, enermax, ocz, or xfx. You need to check the 12v rail rating in amps before deciding on a power supply change. I wouldn't use one with less than 30 amps on a single 12v rail, or 22-24 on dual 12v rails.