The answer is "Yes" to all of your questions.
If all you are backing up is the one server and the XP machine itself. you would need
the base serial
one RAWS (Remote Agent Serial)
one Exchange Serial
Any remote ServerOS machine will require a RAWS. You can backup remote WorkstationOS machines, which require the agent for Registry/SystemState, but it does not need to be licensed. You can do a "silent" install on any XP or W2KPro machines you want to backup See http://seer.support.veritas.com/docs/265736.htm