Microsoft Knowledge Base Article 307900 contains the following summary:
Windows XP Professional supports a superset of the Group Policy features
supported by Windows 2000. The new features are implemented through updated
client-side extensions, .adm files, and an updated Group Policy snap-in.
This article describes how to upgrade a Windows 2000 Active Directory Group Policy object (GPO) to support the new features in Windows XP, and how to manage such objects.