"For years, if you wanted an inexpensive, but Windows-compatible file and print server, you turned to Samba running on Linux. Now, with the first alpha release of Samba 4, this open-source project is moving closer to becoming a complete Windows 2003/Longhorn replacement.
"Since Samba 3 arrived in 2003, Windows network administrators have been able to use Samba and Linux as a drop-in replacement for an NT file/print server. You could, and many have, used Samba in place of an NT PDC (primary domain controller)..."