You need to install J2SE v 1.4.2_06 JRE
[includes the JVM technology].
How to do this you can read in the installation instructions
Make a link to the plugin folder of your browser, for example:
ln -s /usr/java/j2re1.4.2_05/plugin/i386/ns610-gcc32/libjavaplugin_oji.so /usr/lib/firefox-1.0/plugins/libjavaplugin_oji.so
There are many other post about this, try searching for them