Debian Lenny, the current oldstable, ceased receiving security updates early in February, and now seems to no longer be hosted at the usual FTP mirrors (see, e.g., curl http://ftp.nl.debian.org/debian/dists/lenny/ | less).
Are there any surviving FTP repositories of Lenny that can be used via APT?
As answered at serverfault.com or more verbose at superuser.com, you need to use now archive.debian.org:
deb http://archive.debian.org/debian/ lenny contrib main non-free
deb http://archive.debian.org/debian-security lenny/updates main
To get the GPG key:
apt-get install debian-archive-keyring