Hi,
In fact, the applet jars will be cached by the plugin. You can use the following switches to check what the applet is doing when it downloads from a website.
-Djavaplugin.trace=true -Djavaplugin.trace.option=basic|net|security|ext|liveconnect
If you want a little more control, you can use cache_version. See http://java.sun.com/j2se/1.4.2/docs/guide/plugin/developer_guide/applet_caching.html#algorithm
Saj