I had just finished installing Ubuntu 7.10 on a virtual machine. This virtual machine had no active connection to the internet (which is why this actually happened).

After install, I tried to run the software update service. It said that there were no updates to install. I tried to apt-get install ssh and that failed too. So I tried apt-get update. No updates. Hmmm.

It turns out that if there is no active connection, Ubuntu will comment out all the sources for software in the sources.list file. You can find it here:
cd /etc/apt
nano sources.list
uncomment some of the repositories and save the file
apt-get update