I’m not sure if this is specific to the Ubuntu Live based installs, or if this would apply to any Ubuntu installation. However, attempting to install sun-java6-jre (or sun-java5-jre) has left me with a continuous string of errors until I did this…
ln -s / /cow
It seems as though one of the installation scripts has this path hardcoded in it, and, without it, these scripts fail.
I hope this helps you if you should even encounter the same problem.