First, read about the LDAP login module at http://docs.jboss.com/jbossas/guides/j2eeguide/r2/en/html_single/#ch8.ldaplogin.sect.
You could also search the forums, there are various LDAP-related discussions. There is a wiki entry for using LDAP with the Portla at http://wiki.jboss.org/wiki/Wiki.jsp?page=UsingAnLDAPSourceForPortalAuthentication which mentions the LdapLoginModuleExt.
Next, I would get an LDAP browser (http://sourceforge.net/projects/jxplorer/) so that I could easily find the users and groups. Then I would get the ldapsearch command line utility (available with almost every LDAP server) so that I could validate the settings that I would use in the LdapLoginModule[Ext].
Next, I would use a simple web application that uses the login module to verify that it is working correctly.
Only then would I consider configuring a security domian for the messaging server (http://labs.jboss.com/file-access/default/members/jbossmessaging/freezone/docs/guide-1.0.1.SP4/html/configuration.html#conf.serverpeer), and defining acccess rights on the destinations (http://labs.jboss.com/file-access/default/members/jbossmessaging/freezone/docs/guide-1.0.1.SP4/html/configuration.html#conf.destination.security).