Collection of some hints about Debian installation on my D-Link DSM-G600:

firmware (kernel+busybox)

It will fix various problems, including, but not limited to, problems with web interface in firefox.

http://download.dsmg600.info/people/sala/fwimage-04-sala-20070128

I tried to build firmware from source, but had various problems with building gcc

Debian installation

cd /mnt/HD_a2
export DEBOOTSTRAP_DIR=`pwd`/usr/lib/debootstrap
export PATH=$PATH:/mnt/HD_a2/bin:/mnt/HD_a2/sbin
./usr/sbin/debootstrap --arch powerpc etch /mnt/HD_a2/debian http://ftp.de.debian.org/debian