Work your way through the quickstarts. They should illustrate everything you've asked.
The only question left is still how the Gateway_channel and ESB_channel get linked together?
I noticed that in the jboss-esb.xml, channel_GW and channel_ESB is usually defined/grouped together in the section. So is this means I have done linking the gateway and "internal" listeners already?
JBossESB 4.2.1 Adaptor doc describes the Gateway, but it didn't say anything about how gateway message get sent to the "corresponding" internal listener.
Thanks in advance