Estes são os erros que recebo:
(como você pode ver, eu me conecto à internet a partir do proxy do departamento de educação)
W:Failed to fetch http://au.archive.ubuntu.com/ubuntu/dists/quantal/Release.gpg Something wicked happened resolving 'educf.proxy.tas.edu.au:8080' (-5 - No address associated with hostname)
W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/Release.gpg Something wicked happened resolving 'educf.proxy.tas.edu.au:8080' (-5 - No address associated with hostname)
[CUT OUT SOME RESULTS, TOO MANY LINKS]
E:Some index files failed to download. They have been ignored, or old ones used instead.