sudo aptitude update
sudo aptitude safe-upgrade
sudo aptitude full-upgrade

sudo aptitude install firefox gimp gnuchess
sudo aptitude remove opera skype
sudo aptitude purge kde

sudo aptitude autoclean
#sudo aptitude clean

# /etc/apt/preferences
Package: *
Pin: release o=Debian,a=stable
Pin-Priority: 900

# other repo should have priority < 100 so that it wont replace existing packages

Package: *
Pin: release o=Debian,a=testing
Pin-Priority: 80

Package: *
Pin: release o=Debian,a=unstable
Pin-Priority: 30

Package: *
Pin: release a=etch-backports
Pin-Priority: 33

Package: *
Pin: release o=Debian
Pin-Priority: -1

Package: *
Pin: origin www.debian-multimedia.org
Pin-Priority: 700

Package: *
Pin: origin tuxfamily.org
Pin-Priority: 400

sudo aptitude -t unstable install something from unstable