Modificando e Personalizando source.list

Depois de muita luta achei uma configuração boa para o source.list


# deb cdrom:[Ubuntu-Server 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted
deb-src http://archive.ubuntu.com/ubuntu/ gutsy restricted main #Added by software-properties

# deb cdrom:[Ubuntu-Server 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://sft.if.usp.br/ubuntu/ gutsy main restricted
deb-src http://sft.if.usp.br/ubuntu/ gutsy restricted main multiverse universe #Added by software-properties

## Major bug fix updates produced after the final release of the
## distribution.
deb http://sft.if.usp.br/ubuntu/ gutsy-updates main restricted
deb-src http://sft.if.usp.br/ubuntu/ gutsy-updates restricted main multiverse universe #Added by software-properties

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://sft.if.usp.br/ubuntu/ gutsy universe
deb http://sft.if.usp.br/ubuntu/ gutsy-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://sft.if.usp.br/ubuntu/ gutsy multiverse
deb http://sft.if.usp.br/ubuntu/ gutsy-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://br.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse
# deb-src http://br.archive.ubuntu.com/ubuntu/ gutsy-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
deb http://archive.canonical.com/ubuntu gutsy partner
deb-src http://archive.canonical.com/ubuntu gutsy partner

deb http://sft.if.usp.br/ubuntu/ gutsy-security main restricted
deb-src http://sft.if.usp.br/ubuntu/ gutsy-security restricted main multiverse universe #Added by software-properties

deb http://sft.if.usp.br/ubuntu/ gutsy-security universe
deb http://sft.if.usp.br/ubuntu/ gutsy-security multiverse


deb http://security.debian.org etch/updates main contrib non-free
deb http://http.us.debian.org/debian etch main contrib non-free

# Você pode encontrar mais links de repositórios com #pacotes DEB no:
# http://www.apt-get.org


deb ftp://ftp.mowgli.ch/pub/debian etch unofficial
deb-src ftp://ftp.mowgli.ch/pub/debian etch unofficial
deb http://deb.opera.com/opera/ stable non-free
deb http://www.debian-multimedia.org stable main
deb http://www.winki-the-ripper.de/share/debs/debian etch contrib
deb-src http://www.winki-the-ripper.de/share/debs/debian etch contrib



Vale ressaltar que as chaves precisam ser configuradas com os comandos:
gpg --keyserver subkeys.pgp.net --recv-keys KEY
gpg --armor --export KEY | sudo apt-key add -

onde KEY são os ultimos 8 digitos da mensagem de erro ao executar apt-get update

Também criei e configurei o arquivo /etc/apt/preferences como:

Package: *
Pin: release a=gutsy
Pin-Priority: 700

Package: *
Pin: release a=etch
Pin-Priority: 600

Para versão anterior do Ubuntu utilizava:
#
# deb cdrom:[Ubuntu-Server 7.04 _Feisty Fawn_ - Release i386 (20070415)]/ feisty main restricted
deb-src http://archive.ubuntu.com/ubuntu/ feisty restricted main #Added by software-properties

# deb cdrom:[Ubuntu-Server 7.04 _Feisty Fawn_ - Release i386 (20070415)]/ feisty main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://br.archive.ubuntu.com/ubuntu/ feisty main restricted
deb-src http://br.archive.ubuntu.com/ubuntu/ feisty restricted main multiverse universe #Added by software-properties

## Major bug fix updates produced after the final release of the
## distribution.
deb http://br.archive.ubuntu.com/ubuntu/ feisty-updates main restricted
deb-src http://br.archive.ubuntu.com/ubuntu/ feisty-updates main restricted #Added by software-properties

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://br.archive.ubuntu.com/ubuntu/ feisty universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://br.archive.ubuntu.com/ubuntu/ feisty multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://br.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
# deb-src http://br.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu feisty-security main restricted
deb-src http://security.ubuntu.com/ubuntu feisty-security restricted main multiverse universe #Added by software-properties
deb http://security.ubuntu.com/ubuntu feisty-security universe
deb http://archive.ubuntu.com/ubuntu/ feisty-updates restricted main multiverse universe
deb http://security.ubuntu.com/ubuntu feisty-security multiverse

## Repositório Debian Sarge para instalação do Webmin
deb http://download.webmin.com/download/repository sarge contrib