Sam Gentile's New Portal
If you haven't already, you need to set a bookmark for Sam Gentile's new portal. Sam is a great resource for all things CLR, Rotor, and COM interop. The documents section has a link to his article in MSDN on COM interop, which is one of the best explanations I have seen on the subject. There is also a great PowerPoint that concisely explains .NET, the ECMA standards, the CLI implementations, and an incredible visual explanation of the CLR, assemblies, and garbage collection.