The current windows XP installation contains the system/MB drivers from the current MB. When you try to move the hard drive with the current installation to the new MB, the currrent system drivers will conflict. The best way to start up with the new MB/CPU/RAM is to do a clean installation of Windows XP. Be sure to save personal files to disk or removable drive. Some may suggest doing a 'repair install', but I would recommend a reshly formatted, clean installation of XP. Then load up the new system drivers from the new MB's driver CD.