Exchange 2007 Cross forest, multiple companies

Ok, so I have been searching and have found numerous docs that are close to what I'm looking for, but I either got to a point they didn't work or weren't quite fit.

My issues is in two parts:

1) I need to do a cross forest migration of select mailboxes. Basically, we are getting rid of Exchange servers at the child company level and only going to host the Exchange at the parent company. I have created a new forest and have setup trust relationships with the child company domains. That part is working as my "test" account can log into OWA and look at mail using the domain/user and the password from their actual forest/OU.

Now I need to figure out how to get some, not all, of the mailboxes (again, Exchange 2007 to 2007) from the old servers to the new. I have read article after article about migration, but I'm either no understanding something or I'm looking at the wrong thing.

Couple questions:

1) Does anyone have a clear step by step of migrating cross forest?
2) How do I setup users since they are currently user mailboxes and in the new system they will be linked mailboxes? Do I set them up ahead of time? Will the migration take care of this?

Issue 2:

Once I have all of the mailboxes in the new Exchange, How do I set it up so the GAL doesn't list all the users? Ideally, I would prefer each user to get a list of accounts associated with his/her child company only - or basically, how can the GAL per user only list the other E-mail accounts associated with the individual domain.

Thanks in advance
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mario_andresConnect With a Mentor Messaging ArchitedCommented:

   Here is a link to a very good article.

It would be beneficial to setup a very simple lab environment and do some trial migration run and document your process.  I never used the Active Directory Migration tool, but
Here is a link to a quick Video of how to use the tool.
CompuzAuthor Commented:
Thanks for the help. The lab enviorment worked well
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