.NET Active Directory Wrapper    
Access Active Directory From Your C# or VB .Net Code
 

Active Directory
Introduction
Objects
Object Properties

DirectoryServices Namespace
Introduction
DirectoryEntry Class

How to .. in C# .NET
Create User
Disable User
Enable User
Authenticate a User
Change User Password
Get DirectoryEntry of a user
Get Users in a Group
Get Object Property

Other Resources
References

DirectoryServices References

Mircosoft System.DirectoryServices Namespace from MSDN

DirectoryEntry Members