If you like me was putting of an upgrade from Debian 5.0 Lenny you might find yourself blocked out, because ftp.us.debian.org/debian/dists/lenny doesn’t exist anymore anywhere on the US mirrors. However, I needed to do one last update before getting on dist-upgrade.
Luckily enough I was able to find a mirror in Germany which still has Lenny dist around. So, if you find yourself in my shoes edit /etc/apt/sources.list on your system and replace
then do usual update and then an upgrade. Good luck!