As of January 24, Jaunty Jackalope has been included among the versions of Ubuntu covered by the Medibuntu archive. Medibuntu is dedicated to distributing software such as Real Player or certain codecs that cannot be included in Ubuntu for various reasons, including patent, or legal restrictions in some areas.
Included among other things in the Medibuntu repositories are Adobe Acroread, Real Player, Google Earth and Skype.
The easiest way to add the Medibuntu repository for your version of Ubuntu is to go to System > Administration > Software Sources, click on Third-Party Software, and then add the following:

deb http://packages.medibuntu.org/ jaunty free non-free
replacing jaunty with your distribution name if you are, for instance, using intrepid or hardy.
Once you have included the new repository, make sure you go into System > Administration > Synaptic Manager and download the Medibuntu key. Then, you won’t get errors saying that the other things you download from Medibuntu can’t be authenticated.
Happy downloading!