Not XP, actually Snow Leopard (10.6.8) on a 2006 Mac Mini

. However, Calibre is version 1.48.0. The newer computer is running Yosemite and doesn't have Calibre installed yet, but it will be the most recent version.
So it sounds like it will probably be okay? I do have a backup of it if worst comes to worst, but it's a pretty big library and it would be a pain to have to restore it.