Vista - Looking for an MDI solution with different processes

I want to write something like an MDI application. But it shall not run
in a single process, because the MDI clients shall not block each other
or even crash it all down.

Does anyone know a solution for this?

For example something like a sub-desktop inside of a windows forms
control, where I can handle independent programmes by a separate window
manager. Something that behaves similar to an embedded RDP session or a
virtual PC.

Or a real MDI application that docks external main windows to its empty
MDI clients.

TIA, Markus