I would check that jboss.jar is not corrupt by trying to unpack it, and try with a jdk 1.3.1 version, and try jboss 3.0.1 or 3.2. I don't know what is causing this problem.
OK, i'm gonna try to download jboss 3.0.2 or 3.0.1
but i thought that jboss 3.0 support j2sdk 1.4.0? isn't it?
I even try jboss 3.0 on Win XP with same jdk (j2sdk 1.4.0),
same exception is caught ! i'm thinking in fact that the archive is corrupted (maybe during downloading?)
I'm gonna try with jboss 3.2...
OK, that was in fact due to archive corrupted !
it's "jboss-3.0.0_tomcat-4.0.3.zip" downloaded from jboss.org, anyway i've downloaded jboss3.0.1 and installed it with j2sdk1.4.0 on Redhat 7.3 :
It works fine ! ;-) (finally)