Dejoin Workstation in Active Directory

I have a client who has come with windows vista laptop and it has been joined on one active directory which is not connected to internet and it is far remote he can log in to the user credentials without the active directory but cannot install any programs becouse it will always look for credentials for active directory. Thus i was thinking to remove it from the active directory. I would like to know if there is a way to remove this client form the active directory without the AD not being there? kindly assist.