find out and download quickstart pdf document draft 4 - it is avaiable. U may find information about configuration of a special jboss cmp file jbosscmp-jdbc.xml: datasource mapping, and bean-table, cmpField/row, relations mapping. If u want to change jndi names of your beans - create jboss.xml file for it.
Then, Postgres template conf file is available under the
%root%/docs folder of jboss. Edit this file and put it under the deploy folder. Take attention to the name of this resource - it have to math 'java:/%name%' in the jbosscmp-jdbc.xml file element.
Then, take a look on the server/default/conf file that defines java-jdbc-ds mapping.
It is a good start point. And btw, go and RTFM now.;-)