An initial article (from 2007)
C# Winforms MS SQL Server:
http://www.simple-talk.com/dotnet/windows-forms/controls-based-security-in-a-windows-forms-application/
Some additional ides:
WinForms - Using a custom principal with AspNetDb
http://www.codeproject.com/Articles/84949/WinForms-Using-a-custom-principal-with-AspNetDb