Get a debugger that supports JPDA(IntelliJ, Eclipse, Netbeans, JBuilder, etc.) and then set your VM options. The jboss run scripts automatically pass the options specified in the JAVA_OPTS env variable so that is a natural place to set them. The following are typical settings for JDK 1.3.x and 1.4.x

Sample JDK 1.3.1 JPDA settings

JAVA_OPTS="-classic -Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=y"

Sample JDK 1.4.1 JPDA settings

JAVA_OPTS="-Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=y"

Note: do not include the quotes on win32 systems