I spent quite a while working with ADAM (Active Directory Application Mode) in Windows 2003 Server / XP on a previous project. It's a great way to incorporate an LDAP directory into your application without requiring a full-blown AD installation, or domain memberships. The Windows 2008 Server version has been renamed AD LDS (Lightweight Directory Services), which is a much better name. LDS incorporates several improvements that make it even more attractive, including some very nice performance increases. Bart De Smet
has a very nice guide
to installing LDS on 2008 Server and setting up a useful configuration. Check it out if you've used ADAM and/or have any interested in LDAP.