Debian - Repositórios (sources.list)

Editar o sources.list com Gedit
gedit /etc/apt/sources.list

#segurança
deb http://security.debian.org/ lenny/updates main contrib

#debian
# deb http://http.us.debian.org/debian/ lenny main contrib non-free
# deb ftp://mirrors.kernel.org/debian/ lenny main contrib non-free
# deb http://download.unesp.br/linux/debian/ lenny main contrib non-free
deb http://ftp.br.debian.org/debian/ lenny main contrib non-free

#som video
# gpg --keyserver subkeys.pgp.net --recv-keys 07DC563D1F41B907
# gpg --export --armor 07DC563D1F41B907 | apt-key add -
deb http://www.debian-multimedia.org/ lenny main

#backports - ainda nao foi ligado um backports para lenny
# gpg --keyserver subkeys.pgp.net --recv-keys EA8E8B2116BA136C
# gpg --export --armor EA8E8B2116BA136C | apt-key add -
deb http://www.backports.org/debian lenny-backports main contrib non-free

#este volatile veio ja com instalacao
# Line commented out by installer because it failed to verify:
deb http://volatile.debian.org/debian-volatile lenny/volatile main
# Line commented out by installer because it failed to verify:
deb-src http://volatile.debian.org/debian-volatile lenny/volatile main

depois execute:
apt-get update

e também instale as chaves do endereços
apt-get install debian-multimedia-keyring debian-backports-keyring