ASP.net security with Active Directory

I'm working on an ASP.net (VB) 2.0 site. What I'm trying to do is secure the site so that only certain Active Directory users have access to it. I do not want to require them to log in if possible. I also need to create a few pages to allow certain Active Directory users to define which other AD users have access. Is there a tutorial or site that is out there that can guide me through this? I'm swamped on other high-priority projects and haven't been able to research it much, but the deadline is quickly approaching. Any help or insite is greatly appreciated.