Creating a 2003 AD in mixed mode from the ground up and need to integrate
Exchange 2003/2007 (have not decided which yet).

We will have a forest root domain as a place holder domain, abc.com with a
child domain, na.abc.com holding the user accounts for the domain.
Possibility of haivng an additonal child domain is very likely. The domain
will span multiple physical locations. We will have domain controllers for
the child and forest root domain in 3 sites. Our organziation has two
functions, corporatae and public relations. We would like to create our
Exchange design around this setup, ie if maintenance needed to be performed
on the corporate users, it would not impact public relations users. My
question is, what is the best way to accomplish this.

Scenarios:
1. Create multiple information stores, one for corporate and one for public
relations, however if the Information Store service went down, wouldn't that
take down both instances? If so, that would not work.
2. Create two administrator groups. Not very familiar with this, but I think
this would create two seperate Exchange instances in the organization, so
changes to one group would not impact the other, correct? If not, please
advise. With multiple admin groups, I assume I would need to have multiple
exchange servers. If I have to have two Exchange servers to support this, I
would have to have at least four servers if I were to cluster each
administrator group, correct?

Would I need a seperate domain to accomplish any of this? If I were to
seperate them out into two seperate admin groups or into two domains, would
I be able to have all the users still have same parent domain email address?

Thanks in advance for all the help.