I have a similar issue. I am developing a replacement website that's currently hosted elsewhere. Once the new site is up and running here, we will backup their MySQL DB, restore it to the new site, and then switch the DNS registration.
What I need to know is how to set things up here for testing and "customer" approval before they switch to the new site here. I also need to set up the email as well, since they will need an announcement list for sending mailings to the members. We may switch the DNS registration hosting here as well, but that may not happen immediately.
My goal is to name stuff the same whenever possible (eg: system email addresses), and not interfere with the operation of the current site.
Thanks for any help...