How to: Set up a multi-session PostgreSQL Server on a Mac OS X (10.3.8)?

Greetings:
    I'm a neophyte and can now set up a single-session server within my
account.   What I want to do, is create a separate non-human account
(similar to WWW for Apache) to allow multiple clients (multi-session)
to run against the Server 'postgre' account.
How do I go about doing this?
Is there a step-by-step (setting up account, etc.) guide to do this?

Regards,
Ric.