This can be done by installing Sametime in partitioned mode, however, I would strongly advise against your plan. 5 is simply too many partitions for a standard Windows server. It doesn’t manage the memory well enough, and crashes can be problematic as restarting a single instance isn’t always possible. If you partition on Windows, I honestly wouldn’t go over 3, and that’s pushing it. 2 is about as many as I would want to do in a production environment.
As for replicating the Domino Directory, have your admin server initiate a replication of names.nsf to the other servers on whatever frequency you deem necessary. Usually every hour is sufficient.