Finding Existing People
If you want to find people from another social network, use the Connect your services box on the Windows Live main page. This can also be done by selecting Messenger from the top of the Windows Live window.
When you select an existing social network, you'll be asked to choose your settings, such as viewing status updates in Messenger, sharing your Windows Live status and tagging friends in the Windows Live Photo Gallery. When you've chosen the settings you want, press the Connect button at the bottom of the screen. Log in using your user name and password for the desired social network. If you are not currently a member of the social network, you can join by selecting Sign Up above the list of settings. You can then find new people by searching within each individual social network.
To find existing contacts from email accounts and other networks, select Messenger from the top of the screen and choose Add Friends. Find people by entering their email address or name and pressing Next in the Add People by Name or Email Address text box. This lets you find people in your contact list (which is only useful if you need to find people within a large contact list).
Select a service from the Add People from other services to search from people on any of the applicable networks you're a member of. Windows Live currently lets you add people from Facebook, MySpace, LinkedIn, AOL Mail, Hyves, Gmail, Hi5, Tagged, Outlook and additional Windows Live accounts.