After getting Cacti up and running successfully on Fedora Core 5, I had a problem with the graphing. Caci was receiving the SNMP data correctly (the graph legends would show the proper data values), but the actual neato colors and lines were absent in the graph image. After some research I found a fix: Everything in the rra file must be owned by the cacti user, or the user running the poller crontab. Pretty simple:
chown -R cacti.cacti /usr/share/cacti/rra
Once the rra files were owned by the cacti user, the graphs started to appear in all their colored and lined splendor!