The Jez McKinley Wiki

if when you add a source to apt you get :

GPG error: http://ppa.launchpad.net jaunty Release: 
The following signatures couldn't be verified because 
the public key is not available: NO_PUBKEY <KEY>
W: You may want to run apt-get update to correct these problems

then run :

gpg --keyserver subkeys.pgp.net --recv <KEY>

If you see a line like :

gpg:               imported: 1  (RSA: 1)

then run:

gpg --export --armor <KEY> |sudo apt-key add -

if it responds with 'OK' then you should be sorted.