A tarball of all relevant files can be found here.
All files are hereby released under the GNU Public License version 2, and are apparently copyrighted by Oregon State University.
There are 2 major parts to this system. The first is the cf.classes file, which simply describes which hosts belong in each class. The relevant classes are as follows:
service_munin_host = ( larch )
service_munin_node = ( binhost columbia coos fir fraxinus g1 g2 g3 g4 )
package_munin_node = ( service_munin_node www_phpbb_com )
The second part is the cf.munin file, which holds all the rules that each host should follow. Included are several support files that do such things as generate the munin.conf file, since that is difficult to do by hand.
If you have any questions about how it’s implemented, feel free to drop me a line on IRC and I can help explain things to you.