You can also have multiple installations of multiple versions of Oracle each with multiple databases, all on the same server. For example, I have a test server with Oracle 8.0.4, 8.0.5, and 8.0.6 all on the same machine. When you do this, set up a folder d:\Oracle and then separate homes for each D:\oracle\ora804, d:\oracle\ora805 etc. to kewep the versions straight. For each installation - I have set up at least one database. The tricky part is that you have to use the listener and other utilities from the most recent version of Oracle (in this case the 8.0.6 version). I also have another server with an 8.0.5 and an 8.1.6 installation on the same machine - again - use the listener from the most recent version. Disable the other one. Also if you do want to use multiple listeners - you must give unique names to each listener and keep a list of these names handy when you shut down and start up listeners using LSNRCTL.