If you are writting a custom provider for ASP.NET, start with the source. Pun intended :)
Today we released the source code for the built-in ASP.NET 2.0 Membership, Role Management, Site Navigation, Session State, Profile, Web Events, and Web Part Personalization providers (basically all of the built-in providers that ship in the .NET 2.0 Framework Redist).
Read Source Code for the Built-in ASP.NET 2.0 Providers Now Available for Download