It is simply done from the Server/Servers view of the directory. Use the Web button and ?Create Web SSO configuration?. Add the server to the configuration. Make sure they are all set for Multi-Session authentication in their server documents. They must all be in the same Domino domain, and they must all be in the same DNS domain. The SSO is based on DNS domain. You can only have one SSO in R5 Domino domains.
Dig Deeper on Domino Resources - Part 7
Related Q&A from Michael Lazar
Learn how to easily keep track of the numbers of incoming and outgoing Lotus Notes email messages to and from your Domino server each day. Continue Reading
Discover what steps you can take if your Lotus Domino server runs out of disk space and you have issues sending and receiving Lotus Notes email ... Continue Reading