What are the transition options available in Exchange Server 2007

We can make transition in following options

Single forest to single forest – you have an existing single forest Exchange 2003 or Exchange 2000 topology, you can transition to a single forest Exchange 2007 organization.

Single forest to cross forest – If you have an existing single forest Exchange 2003 or Exchange 2000 topology, you can transition to a cross-forest Exchange 2007 topology.

Cross forest to cross forest – If you have an existing cross-forest Exchange 2003 or Exchange 2000 topology with Exchange servers and mailboxes in each forest, you can transition to an Exchange 2007 cross-forest topology.

Resource forest to resource forest -

Single forest to resource forest -