Last week at one of my live events we were talking about Read Only Domain Controllers, and some of the benefits of using them. I told the group that there was a step by step guide on the TechNet web site.
"An RODC is an additional domain controller for a domain that hosts read-only partitions of the Active Directory database. An RODC is designed primarily to be deployed in a branch office environment. Branch offices typically have relatively few users, poor physical security, relatively poor network bandwidth to a hub site, and little local IT knowledge."
As promised here is a link to the information.