How do I activate Windows Vista and Windows Server 2008 using KMS?
After you set up your KMS activation, by default both physical and virtual Windows Vista and Windows Server 2008 machines will attempt to activate by connecting to the KMS host. You must establish and maintain a minimum number of physical KMS client computers for activation to occur. You must have at least five (5) physical computers to activate Windows Server 2008 and at least twenty-five (25) physical computers to activate Windows Vista clients.