I’ve finally completed the Samba PDC setup for a small office how-to.
This how-to describes how to setup Samba on CentOS 5.4 to act as a primary domain controller for a small office.  I say small because it uses the default Samba back-end for storing the user and group information instead of LDAP.
You can find the how-to at http://www.rainingpackets.com/wiki/doku.php?id=setting_up_a_small_scale_samba_pdc_on_centos.