in 2.4 there is no way to that, all the beans you put in lib/ext and conf/ will be started.
in 3.0 you can manually deploy (install and start) components by dropping them in the /deploy directory with a sar like format or simple service.xml snippet, that starts and stops them. You will need to copy paste the files to start them.
So how do you get the MBean to start automatically? Do you define a start() method and is that automatically called by the MBean server? I can't find any docs on how to do this under JBoss 3.0?
This is described in the Admin & Dev. guide.