viewing exchange resources across forests

So companyB acquires companyA and will eventually all be under domain of companyB.  Down the road, the goal is to have an exchange environment with users from both companies on the B domain.

Right now, we have A users able to send and receive on B domain through combination of AD contacts in domain B and public address of A in B spf record so that part works.

What we are trying to do now is have the ability to view calendars (free/busy) and GAL from B on the A domain.  I have looked around a bit and found that it doesn't seem to be that easy.  A is 2003 and B is 2007 (later we'll merge both to 2010).  I understand the first part is to get the ipsec tunnel working and forest trust setup between A and B.  The exchange part could be an issue.  I've found a posting suggesting to use microsoft inter-org utility but it would only work for public folders; doesn't solve the GAL issue.  Has anyone had to do this before?  If I were to use it for free/busy, would the 2007 B server need a pf store (for 2003 compatibility so our server can see it)?
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Seth SimmonsSr. Systems AdministratorAsked:
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suriyaehnopCommented:
Assume that Company A under Domain A while company B under Domain B.

1. Make sure that both DNS server able to resolve each others.
2. You need establish trust between 2 domains.

So share the GAL/Free busy, you must create a "Linked Mailbox" for User at Company B.

http://technet.microsoft.com/en-us/library/bb123524.aspx
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Seth SimmonsSr. Systems AdministratorAuthor Commented:
As I said, I'm already aware about the first parts to get the network and domains talking to each other.  As far as that article goes, it applies to Exchange 2010 SP2; only 2003 and 2007 are variables here.  Moving to 2010 is another project for another day; management hasn't given us a lot of time to get this first part going.
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Seth SimmonsSr. Systems AdministratorAuthor Commented:
we ended up using quest collaboration services which did what we wanted; seems there is no native way of doing this
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Seth SimmonsSr. Systems AdministratorAuthor Commented:
went with 3rd party solution
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