ASP.NET 2.0 Membership, Roles, forms authentication, and Security Resources:

http://weblogs.asp.net/scottgu/archive/2006/02/24/ASP.NET-2.0-Membership_2C00_-Roles_2C00_-Forms-Authentication_2C00_-and-Security-Resources-.aspx

Using Active Directory to authenticate users to your ASP.NET Web Site:

http://www.beansoftware.com/ASP.NET-Tutorials/Forms-Authentication-Active-Directory.aspx

http://blog.evonet.com.au/post/2008/11/05/Using-Active-Directory-to-authenticate-users-to-your-ASPNET-Web-Site.aspx

http://msdn.microsoft.com/en-us/library/ms998347.aspx