The XP machine has the iTunes library one the C: drive and music stored on an external. I just picked up a Mac and would like to be able to use the same library file to keep ratings and playlist intact. Syncing my iPhone with both machines would be a great thing too. I know it will involve network sharing and writing permissions and whatnot. Every guide i've found on google only has one type of computer or they only explain how to set up library sharing in iTunes.