Put this in sources.list
deb http://packages.leonerd.org.uk/ $DIST main deb-src http://packages.leonerd.org.uk/ $DIST main
Where $DIST is one of testing, lenny, squeeze, wheezy, unstable.
Import the repository key by running
$ wget -O - http://packages.leonerd.org.uk/repo-key.asc | sudo apt-key add -
Then run the usual apt-get update to fetch the package lists.