Pues por fin MS tiene un cliente oficial para varias plataformas (entre ellas linux) ya que ha sacado un cliente web para su sistema de mensajeria instantanea.

http://webmessenger.msn.com

What is MSN Web Messenger?

MSN Web Messenger lets you talk online and in real-time with friends and family using just a web browser! Use it on any shared computer - at school, at work, at a friends house or anywhere you ca not install the MSN Messenger software.

You must have the following to use MSN Web Messenger:
A web browser: Microsoft Internet Explorer 5.0 or later, Netscape 7.0 or later, or Mozilla 1.6 or later, running in Microsoft Windows.
An Internet connection (56 Kbps or faster recommended)
A Microsoft .NET Passport. If you have a hotmail.com or msn.com account, you already have a Passport.
Popups enabled for this web site if you are using popup blocker software like the MSN Toolbar

Note: MSN Web Messenger is the official way to communicate with your MSN Messenger contacts using a web browser.