5 clients, 1 machine.

I'm running 8GB of ram, a 3.0ghz phenom II clocked at 3.3ghz on air with no voltage tweaks at all, and an 8800gt/7600gt set of video cards.

Clock a 3.3 up and really wind it tight, use a better main board than I have and better video cards I can see it running 10 clients.