Section 15.1 calls for mod_ruby installation. As of March 25, 2013, modruby.net is not functional and is owned by some unrelated party.
The following adjustment works:
rm -fR /tmp/*
tar zxvf mod_ruby-1.3.0.tar.gz
If you get a "permission denied" error installing from the tmp folder, copy the entire untarred folder to root directory, then run
chown -hR root:root mod_ruby-1.3.0
and you should be able to continue installation as normal.