AMD X2 6000 Dual Core vs AMD X3 8650 Triple Core

If you like to use other programs while gaming, yes. If you run a stripped OS and strictly use it to game, get the dual.

If you look at the benchmarks here

http://www.tomshardware.com/charts [...] ks,16.html

you will see that even though the Phenom has a better clock per clock performance it will lag behind the higher clocked Dual core Athlons in applications that do not utilize more than two cores. While this chart only has quad core phenoms it's a fair comparison to make for those applications that do not benefit from more than two cores. In the newer charts you can see that tri and quad core phenoms perform the same in those applications

http://www.tomshardware.com/charts [...] ks,31.html

If you get the BE edtion of the X3, you may have slightly better overclocking potential than on the X4s and overclocking it would make up for the gap in performance while giving you even more of an improvement when applications that take advantage of more cores become more common. While one could argue for the overclocking of the dual core CPU, the Windsor core doesn't have much overclocking headroom past 3.2GHz.

Considering that the 45nm Phenoms will be out soon I think you should go with the faster clocked dual core and upgrade to a quad core CPU latter on.