Question : exchange 2003 -2010 co-existing between domains in same forest

I have an exchange 2003 server and a 2007 server in a windows 2003 native domain (resource/parent domain). I just created a new 2008 R2 domain tree, in the same forest, which I will be migrating users to over the next several months. I want to rollout an exchange 2010 server and have it co-exist with my 2003 and 2007 exchange servers; however, I want to install this exchange server in my new sub-domain. Can I do this and still have it co-exist with the 2003/2007 exchange servers in the parent/resource domain?
If it can be done and I think it can, are their issues with moving mailboxes between the exchange servers considering they’re in different domains?

Answer : exchange 2003 -2010 co-existing between domains in same forest

You can have your Exchange Servers at any domain, the only pre-requirement in order to do it is that you need to prepare the domains where you will have these exchange servers and your mailboxes users, and if you are going to make advance configurations, like a Cluster, you shall have your nodes in the same AD Domain

When you move the user from one domain to another it doesn't affect because you are in the same Exchange Organization (Forest)

And remember that it is even possible to move mailboxes from one organization to another (One forest to other) using the new move mailboxes tools native included in Exchange 2007 and Exchange 2010