Just stumbled on this while looking for a decent office app.
I had just updated Quickoffice app and remembered that I had my skydive office suite through my Microsoft live account.
So I logged in and skydive and office works - cool
but I noticed the messenger tab had a number next to it so I tapped it and voila.
A new text pop up with all my contacts who are online, tap one and messenger box opens and I am on msn messenger.
Happy days, it will do until an app for Msn.