What you are doing is called a Knife-edge cutover. You install the BES on a new machine and move the DB.
The users will experince a slight service interuption due to the stopping and starting of services.
Search BlackBerry Technical Solution Center
for knife edge or cutover. You will see the article for your version of BES.
Remember that the logical BES name must be the same. This is not the machine name but the name in the BB Manager.