What you have to do is setup your server as either an NIS or a Kerberos server. Then when you install Red Hat, specify your servers IP as the Kerberos/NIS server and you're done. One thing to note, Kerberos is always better than NIS as NIS transmits passwords in plain text. Here you go http://www.redhat.com/docs/manuals/l...-kerberos.html
Cheers,
cgkanchi