Mi archivo /etc/apt/sources.list :
#deb file:///cdrom/ sarge main
#Stable
deb
http://http.us.debian.org/debian stable main contrib non-free
#deb
http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
deb
http://security.debian.org stable/updates main contrib non-free
deb
http://www.debian-multimedia.org stable main
deb-src
http://http.us.debian.org/debian stable main contrib non-free
#deb-src
http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
#deb
http://security.debian.org/ sarge/updates main
#Testing
deb
http://http.us.debian.org/debian testing main non-free contrib
#deb
http://non-us.debian.org/debian-non-US testing/non-US main contrib non-free
deb
http://security.debian.org testing/updates main contrib non-free
deb-src
http://http.us.debian.org/debian testing main contrib non-free
#Unstable
#deb
http://http.us.debian.org/debian unstable main non-free contrib
#deb
http://non-us.debian.org/debian-non-US unstable/non-US main contrib non-free
#deb-src
http://http.us.debian.org/debian unstable main contrib non-free
#deb
http://security.debian.org unstable/updates main contrib non-free
Leí algo sobre apt-pinning y trabajar con paquetes de varias versiones. Si he actualizado con apt-get update.
No se si actualizar a Debian 4.0 Stable(Etch), ya que Debian informa de algunos errores en la instalación de la nueva versión en :
http://www.debian.org/releases/stable/debian-installer/