Since TKL 12.0 is based upon debian squeeze, you can foillow the same instructions as for Debian.

I found these instructions and they're pretty good: http://codetalk.code-kobold.de/?p=289

1) Edit /etc/apt/sources.list and add the "non-free" repository

2) Update apt so it sees the new packages

apt-get update

3) make sure that apt now sees the new packages

apt-cache search sun-java6

4) Install whatever packages you need

apt-get install sun-java6-bin sun-java6-jdk

5) Make sure that the system knows to use sun java instead of openjava

update-java-alternatives -s java-6-sun

6) Add JAVA_HOME environment variable if desired