"Indigo" and "Avalon" Beta1 RC are available for download at http://www.microsoft.com/downloads/details.aspx?FamilyId=B789BC8D-4F25-4823-B6AA-C5EDF432D0C1&displaylang=en. More info can be found at http://msdn.microsoft.com/Longhorn and http://msdn.microsoft.com/webservices.