Couple comments:
1. For sure go to 2008 R2. Much better, much more options/builtin capabilities.
2. Keep in mind that with TS it is better to scale using more smaller servers than a couple big ones. So it may be better to have several smaller (dual CPU, quad core each, wiht 8GB RAM) than just a couple big (Quad CPU, Quad Cores with 32GB for example).
3. Get a fast disk subsystem.
4. I would expect a 64-bit TS on a Dual CPU, Quad Core CPUs with 8GB-12GB RAM and fast I/O to handle at least 110 concurrent users in your case. Given that, 7-8 servers will easily do it.
5. HIGHLY recommend you using something like HP Rapid Deployment Pack to create an automated way to deploy these servers through an unattended procedure. It is 100% supported by all vendors, it removes the human error factor (that happens even with good documentation) and can be FULLY, 100% automated, from setting up TS, setting IPs, NIC teaming, etc all the way up to every single application. That is how I deploy farms that are larger (like this one).
6. If this is your first venture into the TS world, for a setup this size I highly recommend you getting professional help. TS is not as simple/easy as it seems especially when trying to scale to larger numbers.
PS: I am the guy that wrote the "Terminal Services A to Z" guide. :-)
Cláudio Rodrigues
Citrix CTP
