If you are are still running Debian 5 ‘Lenny’ and require access to the apt repository you may of noticed it no longer works. This is because Debian terminated support for this version of there operating system as you can see from the below new post in February. However you can still access the ‘lenny’ repository by changing the repository in sources.lst

Security Support for Debian 5.0 terminated
http://www.debian.org/News/2012/20120209

vi /etc/apt.sources.lst

remove the old repository including security.debian.org and add

deb  http://archive.debian.org/debian lenny main contrib non-free

now run

apt-get update

you will now able able to get the final updates for lenny and install lenny packages.