I recently had to deal with this due to migrating my laptop from Windows to Linux. Anyway, prior to the migration, I backed up all my music/itunes library to an external USB hard-drive. Then after the migration, I copied it back to the hard-drive. I had to do this as I wanted to do a clean install of Linux that included re-formatting my hard drive. After installing iTunes (via a Windows XP VMWare image no less), I "imported" my music library back into iTunes (iTunes lets you import entire directories containing music). Everything seemed to work fine as I'm able to use iTunes to play music on my computer and sync my iPhone, etc.