Here is some more infor on Terminal Server Sizing:
http://www.workthin.com/tshw.htm
There is no absolute standard, other than what it takes to load a user's
profile. Beyond that it depends on what applications you're running, i.e. a
dual-Xeon 4GB server can host a lot of sessions running Microsoft Office, but
that same machine will host many, many fewer if hosting Visual Studio or
Photoshop.
In my office we run some really memory intensive apps, so individuals can
easily use 100-150MB each, in addition to quite a bit of CPU usage, so we
have a small farm of 4 citrix servers to support only 60 users. In reality 2
of the servers could sustain the entire load w/o much problem, but we chose
to err on the side of safety so we can loose a server w/o much interruption
in our business.
Patrick Rouse
Microsoft MVP - Terminal Server
http://www.workthin.com