I know people will yell at me for this, but in my experience as a GAMER, dual processor machines are completley pointless. For the extra money, I would get water-cooling instead.
My friend wanted to build a dualy but I eventually talked him out of it.
Of course, things like Windows and applications, and rendering program that can use dual processors obvisouly run A LOT better with duals.
99% of games out today can't utilize two processors at once. The couter-arguement to this is that windows will use 1 processor to run itself, and use the 2nd cpu to run the game. Effectivly having 100% of 1 CPU deticated to the game would increase performance. Sounds great in theory, but so does communism.
I say it's not worth it until dual-CPU-utilizing games are more abundent. (Quake II used dual CPU's)