Final answer:
The technician would need to use Windows 7 for all three systems in order to utilize the new HomeGroup functionality.
Step-by-step explanation:
The answer to the question is D. Windows 7 only. Windows 7 is the only version mentioned that is capable of utilizing the new HomeGroup functionality. Windows Vista and XP Professional x64 Edition do not support this feature. Therefore, the technician would need to use Windows 7 for all three systems.