For .NET 1.x, there's really only the System.DirectoryServices
namespace - not much more, unfortunately. That's your basic DirectoryEntry
and DirectorySearcher
classes, and that's about it.....
.NET 2.0 added the S.DS.ActiveDirectory
namespace to handle structural objects like forests, domains, and so forth a lot easier. Check out this MSDN article New Ways to Manage Active Directory using the .NET Framework 2.0 on how to leverage those new capabilities.
For .NET 3.5 and up, there's a new S.DS.AccountManagement
namespace which makes working with principals (users, groups, computers) a lot easier. Again, for an excellent intro, read this MSDN article Managing Directory Security Principals in the .NET Framework 3.5.
Hope that helps a bit!
Marc