Joomla Web Messenger allows you to embed Windows Live Messenger (former MSN Messenger) into your Joomla sites.

Turn your website into a Windows Live Messenger online. This component uses the webservice provided by Microsoft, so you don't have to set up anything. The default values are enough for the messenger to work fine.

Neither you nor your users even have to worry about the password or account name managing, because it is done via Microsoft gateway, simple,secure and fast.
If you want to change the 'look and feel', just modify the default.css file (in the frontend folder of the component).

This component is still on its beta version, but the main functionality (the chat) is fully functional.