Windows Server 2008 R2 includes a new server role, called Active Directory Web Services (ADWS), which is a prerequisite to use the Active Directory Module for Windows PowerShell and the Active Directory Administrative Center. Until recently, you were unable to use the Active Directory Module for Windows PowerShell and the Active Directory Administrative Center unless you were managing a Windows Server 2008 R2 machine. However, Microsoft released the Active Directory Management Gateway Service (ADWGS) in early June to extend this functionality to Windows Server 2008 SP1 (and later versions) and Windows Server 2003 SP2 (and later versions).
ADMGS, like ADWS, provides a Web service interface to Active Directory domains, Active Directory Lightweight Directory Services (AD LDS) instances, and Active Directory Database Mounting Tool instances that are running on the same as ADWS.
I was unable to find a public download for ADMGS. The link on the ADMGS knowledge base page is not functional. However, there is a beta program available through http://connect.microsoft.com.
Additional information on ADMGS can be found here: http://support.microsoft.com/kb/969041.
Additional information on ADWS can be found here: http://technet.microsoft.com/en-us/library/dd391908.aspx.