Part 1: ActiveRecord vs. DataMapper. This would be a quick overview of the two patterns as well as the implementations "ActiveRecord" and the "DataMapper" code that can be used with Rails.

Part 2 DataMapper in Depth: PeepCode already has plenty of screencasts on ActiveRecord. This screencast would be for those who've decided that DataMapper makes sense for one or more of their projects and are moving on from Part1 (above) and now want to take a deep dive into DataMapper, specifically, configuring Rails to use it and how to interact with it from Rails code.