Well you asked a few questions, so let me try to address each individually.
1. For the Terminal Server you'll need one Windows Server License (2000 or
2003)
2. For the clients connecting to the TS you'll need a Windows CAL and a
Terminal Server CAL (TSCAL). Windows 2000 & XP Pro Clients connecting to a
2000 Terminal Server receive a grace connection from the Terminal Services
Licensing Service, meaning you don't ned to purchase one in this instance.
licensing info here:
http://www.workthin.com/tsls2k.htm
http://www.workthin.com/tsls2k3.htm
3. How many users can connect (concurrently) depends on:
A. Hardware, i.e. single or dual CPU, amount of RAM, speed of disk subsystem
B. Waht resources your app requires, i.e. how much RAM, CPU Time, Disk Time,
Bandwidth
C. Bandwidth, i.e. if users will be connecting over a WAN connection users
will need a bare minimum of 26.4Kbps per session, + an additional 4Kbps for
each increase of screen resolution, color depth, adding sound... + printing
& file copy/paste bandwidth. Unually 56-128Kbps per session is sufficient,
inless using streaming video (not recommended) or photo editing software.
Hardware recommendations here:
http://www.workthin.com/tshw.htm
4. 2003 has added features of the core-OS, i.e. cmd line utilities, group
policy enhancements... TS specific enhancements are color depth greater than
8 bit (256 colors), as 2003 can support 16 & 32 bit color depth RDP clients,
whereas this is only possible with the addition of Citrix Presentation Server
on 2000. 2003 TS also supports basic audio and enterprise edition supports
participation with session directory.
5. Citrix Presentation Server has lots of added features that do NOT come
built-into TS, i.e. intelligent load balancing, application publishing,
secure SSL Gateway, Web Interface, Universal Printer Driver, multi-multi
shadowing, policy-based control of session settings, bandwidth throttling,
TWAIN Redirection, seamless windows applications, Java Client, Central
Management Console... If you're deploying many servers, Citrix is usually
recommended, as managing a large TS farm w/o Citrix (or other add-ons) is a
PITA.
Citrix info here:
http://www.workthin.com/citrix.htm
other add-ons here:
http://www.workthin.com/tsao.htm