Active Directory Certificate Services Setup has detected a domain controller running Windows 2000 without Service Pack 3 ...

Active Directory Certificate Services Setup has detected a domain controller running Windows 2000 without Service Pack 3 or later. An enterprise certification authority (CA) cannot be installed when a domain controller is running this version of the operating system. The options to install an enterprise CA are unavailable.

You can install a stand-alone CA now, or you can resolve the problem and install an enterprise CA. To resolve the problem, ensure that all Windows 2000 domain controllers  
are running Service Pack 3 or later, or configure your domain controllers to allow SSL connections from the CA. For information on how to configure your domain controllers, search Help and Support Center.