Preparing for GRT Backup/Restore Job for Exchange

One of the requirements for running a GRT backup/restore of Exchange is to "perform a custom installation of the Exchange Service Packs".  I am following this Symantec tech article: http://www.symantec.com/business/support/index?page=content&id=TECH51740.  I am not sure how to do a custom installation and also whether I need to install all three of the service packs on my media server or just SP3.  I am at SP3 on my Exchange 2007 server running Windows 2003 x64.  Media server is running Windows Server 2003 x32.  

What is a "custom installation" and how do I perform one?  

What are the implications of installing a service pack when the base software, in this case Exchange, is not installed on the Media server?

Thanks, 

Linda