<A HREF="http://www.gamepc.com" target="_new">http://www.gamepc.com</A> build PCs intended for gaming and other uses with dual processors.
Of course dual processor machines can be used for gaming, I regularly use mine for it. There is a catch of course and that is cost. Dual processor machines cost up to twice as much as single proccessor machines. Also because SMP setups tend to be targetted at workstation and server markets they have higher stability requirements and hence the processors usually run just a bit slower that the top of the range single processor equivalent.
<A HREF="http://www.anandtech.com/myanandtech.html?member=114979" target="_new">My PCs</A>