ok, first you have to find the plugin location, and Mozilla's location.
Now, different versions of Java store the plugin in slightly different directories, so you may have to snoop a little.
The plugin should be in the: /usr/java/j2re1.4.1_04/plugin directory.
On my version, its /usr/java/j2re1.4.1_04/plugin/i386/mozilla/javaplugin_oji.so
Then you have to find where Mozilla is located. do a "whereis mozilla"
There should be a "plugins" directory in your Mozilla directory.
You now have to make a symlink from from the java plugin located in the java directory to your plugin directory. It should be something like (as root):
ln -s /usr/java/j2re1.4.1_04/plugin/i386/mozilla/javaplugin_oji.so /opt/mozilla/plugins/javaplugin_oji.so
Of course, adjusting to the locations specific to you.
Then load mozilla and type:
this will tell you what plugins are working.
If you have any problems, post back.