Is CPU affinity really an issue? I just had a server up hosting a 2hr practice session for 5 people, and looking at bandwidth usage in that time shows 80K up and 60K down for the duration. IF that scales, then for 20 people you're going to want 320K(2560kbits)/240K(1920kbits). At least. Mine was set to 40000 down and 10000 up. I've not taken any CPU/RAM readings but it would be interesting to see how many people my little vmware server can host to without falling over. It's only got 2 cores of Phenom II and 2G RAM.