A quick Google search turned up this project which uses both Arduino and rrdtool:
http://benjaminbordonaro.com/bb/page/Arduino-Monitoring-System-with-PogoPlug-and-ArchLinux.aspx
A quick Google search turned up this project which uses both Arduino and rrdtool:
http://benjaminbordonaro.com/bb/page/Arduino-Monitoring-System-with-PogoPlug-and-ArchLinux.aspx