I think you are confusing two different things.
An MBean is a managed bean (part of the JMX spec),
an MDB is a message driven bean (part of the EJB spec).
Thanks! A seemingly trivial answer can really help! ;-)
Also, I am using jboss 3.0.0 and found the compiled code that is discussed in 'http://www.jboss.org/online-manual/HTML/ch13s58.html'. The material is in "lib/scheduler-plugin.jar" and "deploy/scheduler-service.xml". Note that the contents of "lib/scheduler-plugin-example.jar" is redundant; these classes are also in "lib/scheduler-plugin.jar".
This helped me.