Vista/Windows7/Windows Server 2008 introduce a new format for the administrative templates for group policies.  Instead of replicating proprietary ADM files with the group policies, you now create a “central repository” for the ADMX (xml format) administrative templates.  Stored with the ADML files are language specific ADML files (in a subdirectory).  The trick here, is that once you create the central repository then Windows 2008 group policy editors cannot see the old ADM files, so if you have settings you wish to edit you have to create a complimentary ADMX template.  Further, older OS versions cannot read the ADMX files, so you have to be careful to perform a cutover.  Either use ADM files, or use ADMX files and edit the group policies only on newer OS versions. [more]

ADMX step-by-step guide:

“New Windows Vista–based or Windows Server 2008–based policy settings can be managed only from Windows Vista–based or Windows Server 2008–based administrative machines running Group Policy Object Editor or Group Policy Management Console.”

“Group Policy Object Editor on Windows Server 2003, Windows XP, or Windows 2000 machines will not display new Windows Vista Administrative Template policy settings that may be enabled or disabled within a GPO.”

Inside ADM and ADMX Templates for Group Policy

Win Server 2008 Directory Services, Group Policy Templates