If running a manual installation, a hard link needs to be created so that the sample content rpm can find avalon in the '/var/www/avalon/current' directory.
ln -s /var/www/avalon/ /var/www/avalon/current
Install the sample content by running rpm as root with the correct RAILS_ENV for your setup.
RAILS_ENV="development" rpm -i http://www.avalonmediasystem.org/downloads/avalon-sample-content.noarch.rpm
If the install fails and you need to rerun the installation, add the --force flag to the rpm command.