Or maybe you can follow these instructions.
1) Install the latest JDK 5 (or JDK 6)
2) Using a clean, unmodified, installation of JBoss 4.2.3 (make sure you have the one that matches the JDK - there is one version for JDK5 and the other for JDK6), run it and post the foll console output, starting with the run command that you entered.