The team @ Skilldrive http://www.skilldrive.com have put together a really interesting presentation which is targetted at developers but I think it works well for IT Professionals too. If you'd like to understand how the logon process works, how Windows handles encryption and authentication & storing secrets then it's worth a look.
The content includes over one hundred technical slides and the agenda's described as follows:
"Security IDentifier, Logon Session, ACL, Privileges, LSA
Data Protection API
Code based security
Role based security
You can download the slides for free from http://www.skilldrive.com/WindowsSecIntEngOut.zip