http://www.microsoft.com/windows2000/techinfo/howitworks/terminal/TSLicensing.asp

Install the licensing service on both servers but the licenses on one
server.  This will allow temp licenses to be issued to any new clients if
they connect when your primary license server is offline.  Since clients
that already have licenses attempt to renew them 7 days prior to expiration
this means you have a week window for clients that already have licenses.

Hope this helps,