in CSI-Piemonte (http://www.csipiemonte.it/en/home.shtml) we have developed a text Console for installing and managing many JBoss instances on the same host.
Its name is OASIC (Oasi Application Server Adminstration Console) and is constituted by a set of Bash scripts.
We use it for our RedHat linux server-farm's systems. It could probably be used on windows servers with cygwin, but we have never tried.
Separation between different instances is achieved by using different port ranges for each instance. Moreover many JBoss configuration parameters can be modified in order to tune the application server.
Another important feature is that OASIC allows you to create JBoss clusters (partitions) by automatically configuring multicast channels and other necessary settings. Cluster instances, called nodes, can reside on the same host, as well as on different hosts.
Applications' deployment can also be managed via OASIC.
Once you have learned how to use it, is a much more powerful tool respect of java graphical installation console shipped with JBoss.
Obviously OASIC is open source, you can download it from sourceforge: http://sourceforge.net/project/showfiles.php?group_id=218555&package_id=282313
Current version of OASIC works with JBoss 4.2.2.GA and jdk 1.5.0_11. Both JBoss AS and SUN JDK must be manually downloaded, OASIC doesn't redistribute them.
For more information: