4 Steps to installing Java on a Debian system…
Detailed Steps
1 – Get the Java SDK from Sun…
Get it here: http://java.sun.com/
2 – Install the Debian package “java-package” … as root:
# apt-get install java-package
You may also need “fakeroot” … as root:
# apt-get install fakeroot
3 – Create the .deb Package File
This step should be done as a non-root user. Create a temporary directory and copy the java .bin installer file (from Sun) into it. then run the command:
$ fakeroot make-jpkg <SUN JAVA SDK FILENAME>.bin
4 – Install the Java .deb Package … as root:
# dpkg -i <GENERATED DEB PACKAGE FILENAME>.deb
Final Verification
Execute the following to verify that the install worked:
$ java -version
Quick Summary
As root:
# apt-get install java-package
As yourself:
$ fakeroot make-jpkg <java-binary-package-name>.bin
As root:
# dpkg -i <created-package-name>.deb
This article drew heavily from How to Install Sun Java on Debian, which may be found at the following address: http://www.crazysquirrel.com/debian/install-sun-java.php.

More, newer, better information here:
http://ianmurdock.com/2006/05/16/apt-get-install-java-literally/