Jboss 4 is built on JDK 1.4.x and uses JMX 1.2 so it is remotable already.
Only recently is JMX standard in JDK 1.5.
Also use MC4J pretty good open source JMX console.
So you dont have to start JMX through the VM.
Also it seems that Java 5 breaks some thing in Jboss and other application in general...