Samba server
From Linux 101, The beginner's guide to all things Linux.
[edit] Introduction
Samba is the GNU/Linux implementation of Windows file and printer sharing, among other functions such as PDCs (Primary Domain Controllers).
Samba can be used as a replacement for Windows NT4 style domains. It can also join an existing Windows domain (both NT4 as well as Active Directory) to be a file server. It cannot yet replace an Active Directory domain, but can employ an LDAP backend to store user information, passwords, and such.
There is a wealth of information on setting Samba up on the official website, http://www.samba.org/, as well as printed books.

