You can auth against, ldap, samba, NIS, kerbeos and a few others I'm fairly certain.
If you don't need to worry about windows... then that will save you half the headache.
This is a guide to authentication against ldap.
Personally, I have a mixed network so I have a Samba3 PDC with LDAP backend. It's a bit of a learning curve.
You might want to also pick up an ldap browser. (I'm using ldapadmin from sourceforge... but it won't do you much good until your openldap implementation is finished).