From the Terminal Services FAQ at
http://www.microsoft.com/windowsserver2003/community/centers/terminal
/terminal_faq.asp
Q. How do I configure Terminal Services licensing servers for
redundancy or high availability?
A. The right way to achieve high availability is to have multiple
(usually two) per domain (or workgroup or site). Put all licenses on
one licensing server, and leave the other empty. The full one is the
primary licensing server and will service all license requests. If
the primary fails:
* Clients that already have licenses will still be able to connect.
Terminal Services does not look to the licensing server unless a
license is needed.
* Clients with licenses that are about to expire have seven days to
contact a licensing server with licenses, which means you have a week
to get your primary running again.
* Clients that have never had a license will be issued a temporary
license by the backup licensing server and can connect for 90 days.
Once the primary is restored it will replace the temporary license
with a full one at the next client connection.
Having multiple licensing servers that actually contain CALs can
cause several problems.
See the licensing white paper and the two SP2 enhancements for more
information about temporary licenses and license issuance.