There is no such program as Outlook Express 2000.
Do you mean Outlook 2000 or Outlook Express.
You cannot delete anything FROM regedit - it has no meaning - you could use regedit program to delete things from the registry, but that is not the way to uninstall programs.
If it's Outlook 2000 you want rid of, run the Office install program, and remove it. If it's Outlook Express you want to remove, then go to Add/Remove programs - Windows setup - and take Outlook Express out of the list of Windows modules.