TS Licensing and Server 2003

Hi 

We have a client who is looking to extend the support for a Server 2003 environment they have.

The 2003 server they have supports Citrix and have the TS CAL's supplied by a 2003 TS server.
They are unable to find the licensing agreement details to allow the migration of the existing TS 2003 licenses to a 2008 TS server

The 2008 TS server we have has available licenses, is it possible for the 2008 TS server to service license requests from the 2003 servers?

Kind Regards.
Garry.

Thanks Garry