[Ianomed]

Possible: yes
Easy: no

It would involve a great deal of screen scrubbing, filtering through all of the HTML pages, extracting details and converting them for vB. Stranger things have been done though, I know people have used a similar process to move from proboards.com hosted forums.

You would also have to issue new passwords to people, as they wouldn't come across. If you have photos/documents uploaded these would either have to be made attachments to threads, or converted to an addon file/photo gallery.

Unless someone has written this already I think you'll have better luck making this a paid request, it's not something I believe many would consider something to write for fun

There's always the even less interesting idea of importing everything by hand, in which case posts would be owned by the copy/pasting member, or restarting and keeping the MSN group as a legacy board.

Maybe someone else has a better idea?