Final answer:
XP mode, which allows users to run Windows XP applications, is available in Windows 7 Professional and not in any of the Home versions or Windows Vista Ultimate.
Step-by-step explanation:
The feature that allows a user to enable XP mode is found in Windows 7 Professional. Windows XP mode is a virtualization feature that allows users to run older Windows XP applications on Windows 7.
XP mode was specifically designed for business and enterprise customers and is not available for Home versions of Windows, including Windows Vista Home Premium and Windows 7 Home Premium. Furthermore, Windows Vista Ultimate does not provide the XP mode feature either, as it was introduced with Windows 7.