Outlook 2010 Features - Social Connector
The all-new Outlook Social Connector connects you to the social and business networks you use, including Microsoft SharePoint, Windows Live, and other popular third-party sites, so you can get more information and stay in touch with the people in your network without leaving Outlook.
For everyone who lives in their Outlook Inbox and would like to bring in social networking stuff. Looks like just LinkedIn for now, but FaceBook, etc. coming soon. Also looks like it can be installed in OL 2003 and 2007.