Question : a migrating domain question

I currently have 2 domains in a single forest with a 2 way trust between them. I have all of the users and computers in domain a, where there is also 2 branch offices with domain controllers. In domain b there is a domain controller and an Exchange server. What I want to do is move domain a to domain b and break the trust and only have one domain. I have installed the admt tools and read the documentation, but I still have a few questions.
1. Is it possible to move everything and create a new Group Policy afterwards?
2. To move the domain controllers, do I have to demote them, move them, then dcpromo them to the new domain?
3. Will this affect Exchange in any way? Exchange is already in domain b.
4. Anything I should be looking for to break?
I am moving the domain from a Win 2003 to a Win 2003R2 and all of the workstations are XP service pack 2 and 3.
Thanks!

Answer : a migrating domain question

1. Sure.
2. Yes, DCs cannot be moved between domains (they *are* the domain).
3. Given that you're moving to Domain B, no.
4.

Always :)

If you want permissions to work across the trust during the migration check out SID Filtering (on the Trust).

Groups, Users and Computers can all be migrated and it generally works best in that order. Groups and Users can be migrated more than once (synchronising group membership, etc).

Depending on size, some computers will fail to migrate. Make sure you know what to do if they fail.

Passwords on user accounts will migrate if you configure the necessary components.

Anything more complex than file servers and DCs running in Domain A?

Chris