In an installation of JBoss you already have three different "configurations/server", that is if you just downloaded the zip and unzipped it. Those configurations are "all", "default", and "minimal". When you can "run" from the bin directory you are starting up the "default" server. If you wanted to start up the "all" configuration you call "run -c all"
You can always have more than one configuration running at the same time, hence you "multiple users on 1 JBoss server" it should really be called "multiple users on 1 JBoss installation". You can always copy any of those configurations and past it in that same "server" directory, and give the new directory a new name, like the developer's name, so If I copied the "default" directory into the server directory and renamed the directory to "sathish" I can now run an instance of JBoss with "run -c sathish"
Now the key here is the ports and the port numbers being used. Because you will have mutliple instances of the server running, each instance must use a seperate set of port numbers. This is easy to configure, but I will leave that for you to find here:
http://wiki.jboss.org/wiki/Wiki.jsp?page=ConfiguringMultipleJBossInstancesOnOneMachine Good Luck and it is very possible.
Mark