Migration of 5.5 Exchange Public Folders

Scenario.

We have a 5.5 Exchange mail server which shares public folders with three remote sites.
We have been informed that our 5.5 server will be migrated to another site /organisation which contains a 2000 exchange server. Leaving the three remote sites in the old organisation.
We are not duly concerned with the migration of the mailboxes but have some concern how the public folders will migrate.
We cannot have any downtime of the public folders because all sites are international with different time zones.

Question(s)

1. Is there a piece of software that will allow the migration of public folders between different mail organisations?
2. If no software is available , what is the best way to proceed?
3. Are there any other best practices?

Rgds..