Beginning today, Windows Live ID is publicly committing to support the OpenID digital identity framework with the announcement of the public availability of a Community Technology Preview (CTP) of the Windows Live ID OpenID Provider.

You will soon be able to use your Windows Live ID account to sign in to any OpenID Web site!

The Windows Live ID OpenID Provider (OP) enables anyone with a Windows Live ID account to set up an OpenID alias and to use that alias for identification at an increasing number of OpenID 2.0 relying party sites-for example: Plaxo, Pibb, StackOverflow.com and Wikispaces.

Windows Live ID OpenID Provider - October 2008 (CTP)

The initial release is a Community Technology Preview (CTP) Release in the Windows Live ID Integration (INT) environment. It is intended primarily for relying-party Web sites and developers of relying-party client libraries, to enable them to test the interoperability of their implementations against the Windows Live ID OP endpoint and flush out any bugs or incompatibilities.

Note that the Windows Live ID OP supports only the OpenID 2.0 protocol.

The Windows Live ID INT environment is separate from the main Production environment, and is for testing purposes only. If you have not already created a Windows Live ID user account for testing in INT, you can do so at http://signup.live-int.com/.

After you have your Windows Live ID account in INT, go to https://login.live-int.com/beta/ManageOpenID.srf to set up your OpenID alias on that test account.

NOTE: INT accounts are for testing purposes only and are NOT intended to be permanent user accounts. They do not allow access to Windows Live services in Production.

Source- Windows Live Dev Blog