Command line utility for user secuirty?

Is there a command line utility out there that will let us add a user to another users security page? What we need to do give NT4.0 domain users access to specific windows 2k active directory users. It can be done through the GUI but it we have 600+ users to do this for. Specifically, we are trying to give NT4.0 domain accounts access to their Exchange 2000 mailboxes and the only way to do it is to make an AD user, disable it, and give the NT 4.0 account access to that users.

Thanks.