Where and how can I add the keyring for netbook-remix?

I've added "deb http://ppa.launchpad.net/netbook-remix-team/ubuntu intrepid main " to /etc/apt/sources.list according to this:
"https://help.ubuntu.com/community/AspireOne#Install%20NetBook%20Remix"

But when I run `sudo apt-get update && sudo apt-get upgrade` and get the following:
$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  cups cups-bsd cups-client cups-common libcups2 libcupsimage2 libmetacity0
  metacity metacity-common
9 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 6087kB of archives.
After this operation, 16.4kB of additional disk space will be used.
Do you want to continue [Y/n]?
WARNING: The following packages cannot be authenticated!
  metacity-common libmetacity0 metacity
Install these packages without verification [y/N]? N
E: Some packages could not be authenticated
$

I'm setting up the computer for a friend and don't want the authentication error message to popup later.