At this stage of the Exchange Server 2007 scenario for System Center Capacity Planner 2007, you define the background load that usually affects Exchange Server by choosing an existing usage profile. If the amount of background load in existing usage profiles is not accurate for a server, you use the Edit Usage Profile task to modify or create a new server template usage profile that contains the correct amount of background load.To define Exchange Server background load
In the Model Editor, open the site that contains the server that you want to define the background load for.
Click the server, and then click Edit server role.
In the Select usage profile list, click the server usage profile that you want to apply to the server, and then click OK.