This was a great article .. helped me understand clustering better. I was looking for a way to add a node into a pre-configured cluster and this article pointed me in the right direction. I am going to use this as reference for my production deploy.
Thank you.

Your Guide to Portal Clustering in WebSphere Portal Server 5.1. Some things in WebSphere PortalServer work well and are well documented. Other things are well documented and work well in theory. Still other things have okay documentation and will work well when all of the WebSphere stars are aligned. Depending on your implementation, Portal Clustering can fit into all three categories.