Take a look at the deployment doc and specifically the multi-forest scenario
at http://www.microsoft.com/exchange/library. It does a much better job
describing it than you'll get in a newsgroup post.
Keep in mind that Exchange doesn't have anything whatsoever to do with IAA
(identification, authentication, and authorization) as that's handled by
Active Directory (sometimes it is proxied by Exchange as in the case of OWA,
but...)
You'll be particularly interested in the RPC/HTTP stuff as well.
> We have two seperate WIndows 2003 Forests/Single Domain
> in each and would like to implement MS Exchange. Can a
[quoted text clipped - 4 lines]
> we would like to have access to from both Domains.
> Suggestions?