Does it work on 2000 Professional? I am having the same issue and in description says that it has been tested in Windows XP and 2000.
The script appears to not work on windows 2000 professional when attempting to unjoin to a Windows server 2008 domain, when it is run, I get an error "Object doesn't support this property or method: 'objComputer.UnjoinDomainOrWor kGroup' "