I find AMD64 works really well. It handles lots of processes and I/O. I was using AMD64 X2 3800 last year and there was no noticeable load with 30 users. Everyone felt like they had total control. I think AMD's on-chip memory controller is better than Intel's off-chip bottleneck. The important thing for a good terminal server is plenty of RAM. Fortunately, prices are low this year. You want a minimum of 50 MB per user + some for the OS and sercices. This year I run my lab of 24 seats with 2 gB just fine with an old Xeon. It is maxed out with 100 mbits/s (my bottleneck) because my new networking stuff has not arrived yet. It is a great time to use LTSP with the prices of gigabit/CPU/RAM/storage all very low.