Integrating Active Directory with Linux / UNIX
Applies to Windows 2000, Windows Server 2003, Windows Server 2008, and Windows Server R2
Microsoft's Services for Unix
Microsoft's attempt to integrate with Unix and Linux is available through Services for Unix (SFU). Starting in Windows Server 2008, SFU has been built into the operating system. If you have Windows Server 2003, there is Windows Services for UNIX Version 3.5.
Centrify
Active Directory-based authentication and single sign-on to cross-platform systems. Centrify Express can be used to deploy for integrating UNIX, Linux and Mac systems with Windows.
Additional Resources
Authenticate Linux Clients with Active Directory
Windows Security and Directory Services for UNIX Guide v1.0