Installing the JRE on Ubuntu, with alternatives support
ellioth's blog entry on upgrading to Dapper Drake (ubuntu 6.06) makes it sound safe and simple to do, so maybe I'll take the dive. However he talks about installing Sun's Java on the system.
As he mentions, and as we pointed out on the jdk-distros site getting the JRE there is pretty trivially done. Getting the JDK installed is a little less trivial, just poke around in the synaptic package manager and you'll find it.
As for update-alternatives ... there's a command, update-java-alternatives that takes care of switching the whole set of Java related commands together. It would, after all, be rather confusing to have the plugin alternative be from one vendor, and the java alternative from a different vendor.