See tip 5442 for a Windows XP version of this tip.
Microsoft Knowledge Base Article 287506 contains the following summary:
After you run either the Sysprep (Sysprep.exe) or Riprep (Riprep.exe) utility on a host computer to prepare it for cloning, you may want to undo the changes that Sysprep made to the host computer's registry so that the Mini-Setup Wizard does not run when you restart the computer, thereby returning the host computer to its original state prior to the use of the Sysprep or Riprep utilities.
This procedure is useful if the Mini-Setup Wizard causes the original computer to stop responding (hang), thus preventing Setup from finishing. This will allow you to troubleshoot the root cause of the inability of the Sysprep to successfully complete, after which point you can re-run Sysprep or Riprep.
You may also want to use this procedure if you accidentally run Sysprep or Riprep against a Production System and you did not want to change the Security IDs (SIDs) or any of the configurable options for which Mini-Setup Wizard prompts when you next restart the original computer.