We are going to be doing a migration from Exchange 2003 to 2007 relatively soon. We are in the planning phase. This post was very helpful in answering a few questions I had- http://serverfault.com/questions/34773/exchange-server-2007-setup
But I have another one- A little background first. We are planning on clustering 2 Mailbox servers using CCR and Windows2008 cluster technology. We will have a 'front end' which is where our Hub Transport and Client Access server will reside. We already have a pair of clustered Ironport boxes which handles our Edge Transport server roll.
I believe I've read enough about the install where I believe it will be fairly painless, but the part that confuses me is this- At what point do we actually join into my existing 2003 architecture? Before I setup the CCR cluster or afterwards?