There are 2 types of licenses you need to be concerned about:
1. The OS License. You need a LICENSE for each server on which you have Win2K Server installed. A License does not necessarily mean physical media (CD). If you already own one copy, you can go to a Microsoft Authorized Reseller and buy just a License for a second copy. This is slightly less expensive than buying a full copy of the software. On the Microsoft Website a full copy of Win2K Server with 5 CALs costs $999.00 (smallest package MS sells). A Win2K Server License Pack (only a License, no media or manuals) costs $871.00.
2. The Client Access License (CAL). There are 2 CAL licensing modes - Per-server and Per-seat. Per-server mode requires a CAL for each concurrent connection on each server in your network. Per-seat mode requires a CAL for each client computer physically connected to the network regardless of number of servers. The mode you choose greatly depends on how your business operates. CALs average between $35.00 to $40.00 each depending on how many you buy at a time (usually in groups of 5).