The display protocol does NOT affect the amount to RAM consumed by a session,
however it can affect the amount of bandwidth used.
The RAM consumed is determined by the applications being used + about 4MB
for each session. Since many programs share memory and servers don't scale
linearly, you can't just multiply the apps times the number of sessions to
get an accurate idea of how your server will scale.
That being said, you have to keep in mind that for user processes, you only
have access to 1/2 of the total system RAM, as the other half is dedicated to
system processes.
The only ways to accurately forecast your hardware requirements are to test
with actual user sessions (via script or load testing application) or to
bring up a TS and add a few sessions at a time with real users and monitor
the system resources against your know baseline (with no interactive user
sessions).
Hardware recommendations, system scaling & load balancing:
http://www.workthin.com/tshw.htm
Patrick Rouse
Microsoft MVP - Terminal Server
http://www.workthin.com