HOWTO Forge has another HOWTO on configuring aq Samba PDC using OpenLDAP. This time it is about Samba running on Ubuntu 7.10 (Gutsy Gibbons). From the article:

This document is a step by step guide for configuring Ubuntu 7.10 as a Samba Domain Controller with an LDAP backend (OpenLDAP). The point is to configure a server that can be comparable, from a central authentication point of view, to a Windows Server 2003 Domain Controller. The end result will be a server with an LDAP directory for storing user, group, and computer accounts.

You can read the complete article at www.howtoforge.com.