I guess you aren't looking to replace the NT domain controller with a Samba machine?
If you want to use the Samba machine as just a file server on the domain, then you would need to use domain security, yes. You will also need to tell it the name of the domain, and which servers to query for authentication information.
This has some information on a basic setup.
It is pretty outdated, but then, I guess any NT domain information is probably going to be pretty old at this point.