Active directory working with sql server

Question

I have a c#.net 2008 desktop application that I need to add logic to authenicate who the user is. I am going to use windows authenication to connect to the active directory to verify the right of each person by group. Thus I have the following question for a desktop application;
1. Do you know of a reference of that has a desktop form accessing the active directory? The only one I know about is an asp.net applcation accessing the active directory.
2. In this application, I would like the windows desktop application to pass the authenication(active directory) information to sql server 2008 r2 by either user or by group.
Thus I am wondering if you can point me to some references (links and/or urls) i can use to accomplish these tasks or part of these tasks.