There are two ways to install Sun JDK6: create a deb package or try the Debian provided package (which failed as of Nov 07)

Create a Debian package from the JDK install file

to create a deb pkg (taken from this page):

sudo apt-get install java-package fakeroot

download latest java-package from here and install it

sudo dpkg -i java-package-XX

Make sure the jdk install file from sun is available and run

fakeroot make-jpkg jdk-XX

install the package

sudo dpkg -i sun-j2sdk1.6-XX

Install the Debian JDK package

from this page:

echo "deb http://mirror.aarnet.edu.au/debian/ unstable main non-free" >> /etc/apt/sources.list
apt-get update
apt-get install sun-java6-bin sun-java6-jre fastjar

Unpacking replacement libc6 ...
/bin/sh: relocation error: /lib/tls/libc.so.6: symbol _dl_out_of_memory, version GLIBC_PRIVATE not defined in file ld-linux.so.2 with link time reference
dpkg: warning - old post-removal script returned error exit status 127
dpkg - trying script from the new package instead ...
/bin/sh: relocation error: /lib/tls/libc.so.6: symbol _dl_out_of_memory, version GLIBC_PRIVATE not defined in file ld-linux.so.2 with link time reference
dpkg: error processing /var/cache/apt/archives/libc6_2.7-8_i386.deb (--unpack):
 subprocess new post-removal script returned error exit status 127
/bin/sh: relocation error: /lib/tls/libc.so.6: symbol _dl_out_of_memory, version GLIBC_PRIVATE not defined in file ld-linux.so.2 with link time reference
dpkg: error while cleaning up:
 subprocess pre-installation script returned error exit status 127
Errors were encountered while processing:
 /var/cache/apt/archives/libc6_2.7-8_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)