If you're already running linux you'll probably want to integrate our java changes rather than re-install.
These instructions are based on Ubuntu 8.04 Hardy Heron (the version the cd is based on). This process will vary between distributions.
From a terminal run:
sudo apt-get install openjdk-6-jdk
This will install java on your system
Programs in first year java rely on extra classes and jars not part of normal java.
This will download a script that sets the classpath to include the jars/class we just downloaded. This script is ran for all shells.
The above is how we added the java support onto the image used to build the live cd. For more about how the live cd was actually constructed read help.ubuntu.com/community/LiveCDCustomization