Repository of .qtz s in system files? Apparently there is a place within the OS's system files that have lots of .qtz s that you can use for your desktop background. 

Could someone tell me the location of the files?
Open Terminal and run locate qtz to get the list for your system. You may need to install Xcode to get the full set, with the added benefit of being able to run "/Developer/Applications/Quartz Composer.app" to develop your own.