I don't know anything about MacOSX, but I know how frustrating it can be to try and get things going. Much of the help I used was from different platforms, so I figure I'd try to help anyway.
I'm wondering what JDK you're running. You said 1.3.1, but is it 1.3.1_00 or _02? If so, try 1.3.1_04. I've seen several wierd (and fatal) problems go away for myself and others with that upgrade.
Other things I'd try would be to make sure your environment variables are all squared away. You may find one of the following links helpful:
Good luck, if you figure out what it was please share so others can benefit too.
JBoss worked very well for me on OS X 10.1.5.
Do you use the following values?
setenv JDK_HOME /Library/Java/Home
setenv JAVA_HOME $JDK_HOME
I have just upgraded to Jaguar, and have not tested extensively there yet.