How do you guys keep your iTunes libraries sync'ed between multiple computers? I need the ability to keep libraries sync'ed up between my iBook and a PC. In the future, another Mac will be thrown into the mix. If I rip a CD on either computer, or download songs and add them into my library on either computer, I'd like them to be copied to the other computer(s) and added into the iTunes library during the next sync. Up until now I've just shared libraries on each computer, but I really would like to have all the files on both. Is there a program to do this?