I find the one for PostgreSQL to be the easiest for someone to learn since PostgreSQL is easily downloadable and federation is done through JDBC. The one for Netezza has all the technical information you need, but could use a few more examples such as what the Netezza driver name might be and the common directory name for where to copy it to (e.g., sqllib/bin?). We'll see what we can do. The one for IMS requires you be at IMS 11 or higher since it relies on IMS's Universal JDBC driver. And yes, for IMS, you can use InfoSphere Classic Replication Server to federate DB2 with IMS as well as other z/OS data sources such as VSAM, ADABAS, and CA IDMS.
If you give any of these a try, feel free to ask questions in the message board section of the InfoSphere Federation Server group in developerWorks.