Are there any tutorials on how to load custom archive file formats as file systems in Windows Explorer, similar to CAB and ZIP files?
I tried searching for namespace extensions tutorials, but it appears to be a different thing.
See this project - Mini Shell Extension Framework.
Most important for you is first part, from project description:
In order to show how to use the classes and to provide a sample of how to create a shell extension, the code includes a small sample that can open .vvv files. VVV files are just renamed .ini files that act as a container. Most shell extensions are container views (for example, the Windows .zip and .cab shell extensions).