Samba has beta support to be a domain controller. It works, but that is about all I will say about it. That is why we still have an NT PDC here. The next version of Samba (2.4 I believe) is supposed to have full functionallity as a domain controller. The current version does allow most of what you are asking, but it doesn't always work correctly.

If you only have a couple of puters, I wouldn't worry about making a domain. If you really want user authentication, go with kerbos. As far as login scripting, well, it can be done with samba, but do you really need it? Isn't it just as easy to create a batch file that runs at startup to do the same thing?