1) I don't think that there is any documentation available that is specific to 4.2.0. If you are trying to understand JBoss AS by reading documentation, stick to 4.0.5. (Others have already complaint about this lack of documentation.)
2) 4.0.5 comes with Tomcat 5.5 embedded. 4.2 uses the newer JBoss Web Server (sort of Tomcat 6 plus support for the Apache Portable Runtime). So yes, JBoss AS does have its own servlet container.