I'm not sure entirely of what you mean by "join an NT domain" but essentially all you need to do is edit smb.conf (once you've installed samba) and add the name of your NT domain to the line marked:
Other than telling you how to build samba from scratch, that's all I think you'd need to do. There may be another couple of bits to configure (passwords, ids etc...) but that's the main part for NT interaction.
There are loads of HOWTO's on the web, try:
for a good starting place.