http://developer.apple.com/java/faq/#anchor2
^-- this says Java 1.5.0 will never be ported to Mac OS 10.3. It will only work on Mac OS 10.4, which isn't yet available, and which I would have to pay at least USD 100.00 to buy if I wanted it, which I don't.
Why don't you try rewriting your simulator in Python? Python is the easiest language to learn. I'll bet in a mere three hours you will be happy with the new simulator you've written.
Also, the result will be more portable. <wink>