You can use the examples at java web, examples j2ee 1.4, and there you will see at the bundle packed a lot of examples, including MDB. The thing is that you have to write the proper deployment descroptors.
>From: "J. Patrick Bedell" <email@example.com>
>Subject: message-den bean example?
>Date: Thu, 16 Jun 2005 19:19:36 -0700 (PDT)
> I'm trying to develop a message-driven EJB, and having some
>difficulties. Are there any examples of Geronimo-deployable
>message-driven beans that are available for download?
> Thanks in advance for the help!