This post discusses how to uninstall Windows 7 and revert to your previous operating system. “Uninstalling Windows 7 is only possible if “You used the Windows 7 installation media to install Windows 7 to the same hard disk drive on which you had Windows XP, Windows Vista, or another version of Windows 7 installed. In this scenario, the Windows 7 installation will have created a Windows.old folder that contains your previous operating system and personal files. This Windows.old folder is in the root of the Windows partition. If the Windows.old folder was indeed removed and cannot be restored, the uninstall process of Windows 7 is not possible.”

Full Article: KB971762