Get Users from Domain and Active Directory -PLEASE HELP

Hi...

Please help me to get users from AD and Domain-
1.
Domain from-
HttpContext.Current.User.Identity.Name

2.
Domain From-
Environment.UserName

3.
Users from Active Directory.

I want these list is a datatable and display them in a gridview.

I have users in-
Control Panel -> Programs and Features -> Turn windows features on/of -> Windows Features dialog box.

PLease help. It is urgent.