Vista & XP mixed Term Serv printing

We host our software for about 100 of our clients on 2003 R2 servers. Most of
them RDP in from XP machines, but in the last few weeks we have been getting
a mix of XP and Vista machines from the same office. When this happens, we've
been unable to get printing to work on both machines when they need to print
to the same printer. The printer in question today is an HP 6210 (an
All-In-One printer).