Microsoft has announced the immediate availability of the Windows Live Messenger Web Toolkit (MWT) Version 3.7 . The Windows Live Messenger Web Toolkit enables developers to integrate and enrich their Web-based applications with Windows Live Messenger.

V3.7 improves the Messenger Web Toolkit by adding the following.

• Offline IM – Users can now IM offline contacts, just like they can in the Messenger desktop client.
• ASP.NET Ajax Library Integration – Starting in V3.7, the Messenger Web Toolkit UI Controls are built as ASP.NET Ajax Library (http://asp.net/ajaxlibrary/) controls.  This means you can add MWT Controls to your pages using standard declarative and programmatic methods of ASP.NET Ajax Library.
• Improved Application Contacts – We’ve improved application contact functionality to work better based on feedback we received in V3.5.  Application contacts defined on a page no longer are carried across to new pages.  This helps applications avoid hitting the 250 contact limit for application contacts.

Though its not supported for the latest Chrome 4 or Beta5 but it has added support for Firefox 3.6 and Chrome 3.

Links :

• Give it a try
• Documentation