Today Angus Logan announced the availability of Windows Live Messenger IM Control & Presence API:
"The Windows LiveT Messenger IM Control lets people on the Web reach you in Messenger by showing your Messenger status on your web site, blog, or social networking profile. The IM Control runs in the browser and lets site visitors message you without installing Messenger first. It is supported in IE6, IE7, and FireFox 2.0 on Windows and FireFox 2.0 on Mac OS and supports 32 languages."
Go to http://settings.messenger.live.com/applications/websettings.aspx to create your own or visit Via Windows Live to have an introduction to the Windows Live Messenger IM Control & Presence API.
Enjoy!