Ubuntugeek shows us Conky: An advanced, highly configurable system monitor for X based on torsmo
Read the guide here
Conky is an powerful desktop app that posts system monitoring info onto the root window. It is hard to set up properly (has unlisted dependencies, special command line compile options, and requires a mod to xorg.conf to stop it from flickering, and the apt-get version doesnt work properly). Most people cant get it working right, but its an AWESOME app if it can be set up right done.