I must admit I find licensing a huge headache as well, especially on W2k.
I believe you are correct - you require a Windows NT/2000 license for each non W2k/NT DEVICE that logs onto the TS.
You only require a Citrix license per user/connection, so more than one user can log in at one device using one TS license, but 2 Citrix licenses.
This article may help
From one of Microsoft's whitepapers (I've lost the link - if anyone has it, could you post it here, please
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There are 3 licenses needed when connecting to Windows Terminal Services, and you always need 3! If you do not have the three licenses listed below then your Terminal Services are not properly licensed.
1. The server license
This may be Windows NT® Server 4.0 Terminal Server Edition or Windows 2000 Server with Terminal Services enabled in application server mode.
2. A Windows NT 4 Client Access License (CAL) or Windows 2000 CAL
The CAL must be the same version or higher as the server being used. When using the Server CAL to support Terminal Services you may only do so in the Per Seat mode. For further details on per seat, per server and per processor licensing see the licensing brief on that topic.
3. Either a) a Terminal Server CAL (version to match or be higher than server being used) OR b) Windows NT Workstation 4.0 or Windows 2000 Professional installed on the desktop itself (version to match or be higher than server being used example Windows 2000 Pro can connect to Windows NT 4 TS, but Windows NT Workstation 4 would need a TS CAL or upgrade to Windows 2000 Pro to access Windows 2000 Server.).
Note: Terminal Services is licensed on a per-device basis and is not available on a per-server or per-processor use with the exception of the Terminal Services Internet Connector License explained below. Each device, whether it connects directly to the terminal server, or indirectly via another server, requires the appropriate licenses to be assigned to it.
Hope this helps