Like Windows Server 2003, Windows XP has several editions:
Windows XP, Home Edition The operating system designed for home users as a replacement for Microsoft Windows 3.x, Windows 95, Windows 98, or Windows Millennium Edition (Windows Me)
Windows XP, Professional Edition The operating system designed for business users and as a replacement for Windows NT Workstation or Windows 2000 Professional
Windows XP Professional is the only edition intended for use in Active Directory domains. It includes extensions to Group Policy that require updating the Group Policy Objects (GPOs) in a domain using servers running Windows 2000. In a domain upgraded to domain controllers running Windows Server 2003, however, ...