I just now successfully deployed CAS 3.4.2 in Jboss6-m4 Should be similar for Jboss5.1.x. Several things:
1. add a jboss-scanning.xml {code:xml}
<scanning xmlns="urn:jboss:scanning:1.0">
<path name="WEB-INF/classes">
</path>
<path name="WEB-INF/lib/jdom-1.0.jar">
<include name="org.jdom" />
</path>
</scanning>{code}
This is to avoid a continual StringIndexOutOfBoundsException when the scanner comes accross the jdom.jar file and scans a class in the root package.
2. Use maven's pom war overlay feature and do an overlay of your own version of web.xml.. just take a copy of the existing web.xml and remove all references to Log4j and Log4Configurator.
3. Remove from WEB-INF/lib all log4j, slf4j, xml-apis, hibernate-jpa. These will cause numerous errors as they conflict with jboss provided classes and Jboss provided logging.
4. Also I simply deleted the WEB-INF/class/META-INF/persistence.xml as it was causing jboss to complain about compliance. You might need this if you are features of cas that are persisted. Also you may be able to just ignore presistence.xml using the jboss-ignores.txt here http://community.jboss.org/wiki/JBoss5custommetadatafiles, I din't try the ignores approach.