I don't believe this is possible, at least not back with Exchange 2003. Maybe 2013 has some functionality around this with Powershell, but not back then.
You can't simply change meeting organizers. At a minimum this "script" would have to find the meetings, catalog the meetings, then delete and recreate the meetings with the new organizer, which would in turn cause new meeting invites to go out to the recipients. I've never seen a script such as this in the wild, especially when talking about Exchange 2003.
However, here's my advice:
Just inform the user to start using the new mailbox going forward for new meetings, and to let people know that they are using this new mailbox as the "organizer" so that people don't go "what is this?". For past meetings who cares....and for future meetings if it is a really big deal and they are OK with disturbing the attendees again with a cancellation and then new invitation, then it can be done manually.