title: How to trust a apt repository : Debian apt-get update error public key is not available: NO_PUBKEY <id>
body: <p>Trying to update some repositories on Debian Etch installation and getting the following errors from running "apt-get update"</p>
  
  <pre><code>W: GPG error: http://www.debian-multimedia.org etch Release: The following signatures couldn't be verified because teh public key is not available: NO_PUBKEY 07DC563D1F41B907
  W: You may want to run apt-get update to correct these problems
  </code></pre>
  
  <p>The irony of it instructing me to run apt-get update is a nice kicker...</p>