Java for i386
Add the hoary-extras repository (AddingRepositoriesHowto)
Search for sun-j2re1.5 in synaptic and install it.
NB: the hoary-extras mirrors seem to have problems now (24 aug). JRE an JDK debs (i386) can be grabbed from http://seveas.ubuntulinux.nl too
This will configure the Firefox Java plugin. Alternatively, you can build your own Java package by following the instructions on JavaPackageBuildNewVersions.
Java on other Architechtures
Ubuntu PPC, please see: ["JavaPPC"]. Ubuntu AMD64, please see: ["JavaAMD64"].
Installing the JDK
If you want to install the Java compiler as well as the runtime environment, the easiest thing to do is to [https://java.sun.com/j2se/1.5.0/download.jsp get it directly from Sun]. Take care to use the "Linux self-extracting file" version. Converting the RPM with alien will not work.
Then follow the instructions as set forth on JavaPackageBuildNewVersions to create a .deb file you can install using dpkg.