Here is the free download from the FUN309 PDC2005 session.
Here is the description from the download center
"Speakers: Jim Miller; Thomas Quinn
Most large applications allow customers to provide code to customize the application’s behavior. Examples are ActiveX controls for Internet Explorer and SmartTags in Microsoft Office. Correctly designing the interface between a host and its add-ins requires considering security, reliability, and versioning issues. This session provides prescriptive guidance for designing these interfaces when the add-in is intended to be written in managed code. We show the design and implementation of a general-purpose managed add-in model, as well as a prototype of a tool to help convert existing COM object models into managed add-in models."
I believe this download will only be available for a limited time, so unless you attended the PDC 2005 event and you received the DVD, you better act fast.
For more on the Managed Addin Framework.