From Developerworks, “Building clustered topologies in WebSphere Process Server V6.1”

Learn to use WebSphere Process Server V6.1 to create a clustered “Gold” topology using a template-driven approach. This article shows you how to create the cell and federate two empty nodes to it, create a deployment environment, which is a template for the clustered topology,
and test the topology.

A good step-by-step resource to have on-hand if you are ever put in the situation where you need to create a cluster.