migration to other dom, site, and org

I am in the process of moving 75 users from one exchange server 5.5 w/sp3 to a another exchange server with a different domain, site and organization. I want to keep the old email address for a short time, and move users to start using the new email address. I was told it’s a complicated task, and the only way to do this is by using the Move Server Wizard,available w/sp3. Has any one out there done this type of task? Any help/input you can provided is highly appreciated. Thank you.