Sorry. Until yet, we don't have guides and examples about setting up Samba NT4 PDC/BDC here in our Wiki.
Even if it's outdated and in some places meanwhile incorrect, you can have a look at The official Samba 3.5.x HOWTO and Reference Guide. And surely you will find many documentation on various sites on the internet, describing how to setup.
Of course, you're welcome to write some documentation here, based on the latest Samba versions. ;-)
To clarify a common misconception:
To run Samba as an NT4 PDC/BDC, it's is not neccessary and not recommended, to use Samba 3.x! Each Samba version, including 4 and later, provides all features of previous versions. Samba 3.x is meanwhile in disconntinued state (no bugfixes, no security updates, no new protocol support, no new features, etc.). The Samba team strongly recommends using one of the maintained versions!