How to undelete Active Directory Objects

http://www.petri.co.il/manually-undeleting-objects-windows-active-directory-ad.htm

Windows XP Setup Keeps Restarting

If you cancel your Windows XP setup while it is in process it will reboot and attempt to restart the installation.

Boot to something that will let you edit the Windows registry offline and clear the following keys:

HKLM\SYSTEM\Setup\SystemSetupInProgress
        
HKLM\SYSTEM\Setup\SystemSetupInProgress

There is also a key called 'UpgradeInProgress'