I have browse thru the Samba-3 book and it is really scarry. I don't think it is worth the effort to learn it and then put it to use as a domain controller.

Microsoft Active Directory offers many benefits to manage the desktops such as deployment of policies centrally, software push to the desktops etc. If your company can afford it, do consider using Microsoft Windows 2K3 servers.

Well if Win2K3 servers are just too expensive for you, then simple file sharing should be sufficient.