“You may already be aware that the RSS Visualizer, Arabesque and Spectrum screen savers in Mac OS X are Quartz Compositions. There is actually a whole folder full of other compositions hidden in the Mac OS X system files that can be used as screen savers. If you have the Developer Tools installed, there are even more available to you.”
this is really simple to do and some of these hidden screen savers look pretty damn cool! Read below for more info. 
