"Upgrade" Debian etch to Ubuntu 8.04
It is possible, but don't ask. ;-)
Replace the repository lines in /etc/apt/sources.list and do an apt-get upgrade.
First you have to install dpkg (dpkg_1.13.24ubuntu6_i386.deb or dpkg_1.13.24ubuntu6_amd64.deb) from Ubuntu 7.10 manually because of a new feature.
Then you have to "downgrade" sysv-rc because the etch version claims to be newer, but update-rc.d misses a feature for Ubuntu 8.04.
Then install aptitude:
apt-get install aptitude.
Start several iterations of
aptitude safe-upgrade, note every package that has to be removed.
Start several iteration of
aptitude dist-upgrade, note every package that has to be removed.
Iterate until all packages are upgraded. Do a
dpkg -l | grep etch and adjust versions of these packages.
Re-install important packages that got removed earlier.