I DO know the answer.

Both IE and Netscape fall behind in supporting Java 2.
So they cannot find JApplet. In another word, they don't support
Java Swing

Here are two approaches

1) Dowbload Java Plug-in 1.3 from Sun, install it with
your browser

2) Fall back to java.awt. package, for instance,
JApplet---> Applet
JButton ---> Button.


Now why did it work with Jbuildr 3?
Jbuilder 3 uses appletviewer to parse your Applet.