Installing java platform on your favourite GNU/Linux distro can be very hard to do because it was licensed in such a way that it couldn’t be packaged along with your distro CDs. All that will become history as a group of Debian developers, Ubuntu developers, Sun engineers, Sun lawyers have devised a new binary license form so that it could be bundled along with your CD. So, all you have to do is to do an apt-get install sun-java5-jre.
Other famous distributions like Gentoo, NexentaOS, Belenix, OpenSolaris will also have it soon.
Source: http://blogs.sun.com/roller/page/webmink?entry=jdk_on_gnu_linux_something