When Ubuntu releases expire, the package archive mirror is disabled as well. You will get error messages when trying to access e.g. archive.ubuntu.com or de.archive.ubuntu.com. (e.g. http://security.ubuntu.com/ubuntu/dists/karmic-security/main/binary-i386/Packages.gz not found.)
But the fix is easy:
In /etc/apt/sources.list, simply replace the url archive.ubuntu.com with old-releases.ubuntu.com and you can download your old and outdated packages again! And next time, if you can, try to select a long term support (LTS) release, so you have security fixes for a longer time. Because you warned these packages won't have security updates.