You don't have to do anything special in your application. However, you do have to give certain folders and files the correct rights in your installer.

Yes. The trick is to use the [DllImport] attribute, followed by declarations for each of the DLL's functions and procedures.

//GetUser() returns current user information
MembershipUser myUser = Membership.GetUser();

  

//Returns the UserID and converts to a string
string UserID = myUser.ProviderUserKey.ToString();