This question is coming up a lot in the SBS newsgroups. Basically if you have an SBS 4.x or 2000 server and need to buy CALs for it you will soon find out that they have been discontinued. You need to buy SBS2k3 CALs and use your “downgrade rights“ to install them on the older SBS version.
Sounds simple? Yes… well… not quite. When was the last time you saw something simple regarding licensing? 🙂
The problem is that SBS2k (and prior) used a floppy disk to install the CALs (which is no longer needed in 2k3). To obtain this disk you need to call MS Fulfilment Center and ask them to send the media (small fee). For your convinience, the phone number (in the US) is (800) 360-7561 and the sku of the disk is 807-00144.
By the way… this info is (in part) on the Licensing Faq.