Since Sun's license for Java was not entirely compatible with Debian's policies, the JRE is not available directly in the Debian's package repositories.
Instead, you must download the Java JRE from Sun and create the .deb packages yourself, to comply with the letter of the license. Debian provides a tool "make-jpkg" to make this very easy.
First, install the package "java-package". It is available in the contrib/misc section of Debian package repository. It contains the "make-jpkg" tool and the documentation for it.
Then, download the standard JRE self-extracting package (.bin, not .rpm) from
http://java.sun.com.Now you can generate the .deb packages yourself with a command like
make-jpkg j2re-1_4_2-linux-i586.bin
MK