I just got a second-hand PowerMacG5 which runs up to Leopard. I've got Tiger installed on it but I want Leopard. I've got the box but lost my retail Leopard install disc that I owed years ago. Is it possible that Apple can replace the disc? Can I buy a friends second hand retail disc and use that or do I have to buy a brand new version? (With Windows you need to buy a brand new CD because the license only works with that, OEM versions are illegal to install on a different PC so I'm wondering if the same goes with OS X).