http://channel9.msdn.com/shows/Identity/WIF-Workshop-3-Scenarios-and-Architecture-I/

http://stienessen.net/mixed-mode-adfs-2-0-and-forms-authentication-in-a-single-asp-netweb-application

http://msdn.microsoft.com/en-us/magazine/ee335707.aspx

Windows Identity Foundation is worth a try, imho. Claims based authorization.