CMR relation tables are many to many relationships as described in the spec. This means defining both CMR fields (for each entity bean) as Collections, and of course the multiplicity as many.
The mapping to the database is quite specific to each application server.
For JBoss, all the mapping is done in jbosscmp-jdbc.xml. The relation table is described in a tag named <relation-table-mapping>.
If you are a newbee, I suggest you to download the JBoss IDE under Eclipse, and use XDoclet to generate all this staff. You can have a look to the XDoclet documentation at http://xdoclet.sourceforge.net/.
Also, have a look in the Persistence & CMP/JBoss forum where these specifics topics had been posted many times.
All the ejb stuff I have done so far has been done by hand. I have heard many a good comments about XDoclet but never used it.
I am going use it from now on.
Thanks a lot,