I am about to start a new itunes library using itunes on my mcbook pro. I have an ipod 160 gb classic that I have been using on a windows PC. Do I have to format it to mac? or can I leave it to Windows format so I could use it on the PC in the house? Also, I keep all my music, including my itunes library on an external hard drive. will I be able to access my itunes library on my macbook pro's itunes & the itunes installed on the windows PC? so long as the external hard drive is plugged in, so I could snyc & use my ipod on both computers?