Change default sounds Mac OS X

I'm looking to change some of the OS X default sounds (like the very annoying "boing!" drag-and-drop sound). I'm not talking about the alert sound that can be changed easily via the "Sound" function in System Preferences. I'm looking for the Terminal commands that would enable me to substitute an existing Mac OS X sound for the ones I don't like. (I'm not looking to create or find online other sounds; I'm happy to just use the ones that come with Mac OS X.) Some weeks ago I found a web page that described the necessary terminal commands and also where to find the .aiff files, but I've spent the last week trying to find that page again with no luck. I've also searched this and other fora but have not gotten anywhere. Any help would be much appreciated.