Are you just doing it for remote admin? If so, you do not need a CAL, just enable Terminal services in administration mode. If it is for users to run apps off the server, W2K Pro workstations do not need Terminal Services CALs but all other clients do.
If you are doing this for users to run apps off the server, here's the scoop:
All workstations need W2K Server CALs.
All workstations need Terminal Services CALs also except W2K Professional clients.
Terminal Services CALs run around $80, a little less if you have a MS Select or Open Licensing agreement with Microsoft.