Hi Wee,
By definition every device connecting to a Windows server needs a CAL. However, neither the OS nor the SAP system "counts" them.
Depending on which kind of clients you have (Windows XP/Vista OEM, Volume licenses etc.) you have a CAL included.
So based on SAP users created and other users required in your landscape , you may procure respective CALS.
Hope this helps.
Regards,
Deepak Kori