Well, to answer my own question.....

I fond this article at Microsoft - HOWTO: Logging on CDO (1.x) to Active 
Messaging Session with Default Profile (Microsoft Knowledge Base Article - 
171422)

CDO is not really part of this example, so it applies to MAPI as well. But 
it is a whole lot of code to answer a simple question - "what is my 
default email profile?"

If anyone has a better solution, please let me know!

Mark