Fedex just delivered my beautiful MBP. Unfortunately Leopard wasn't preinstalled, but it did come with the disc. My question: Do I "Upgrade" or "Erase & Install"? Haven't set up accounts or anything; booted from Leopard DVD as soon as I saw the Tiger welcome video. Don't want to lose iLife apps that come installed (no disc for those, I don't think). On hold w/ AppleCare - can y'all help me first?!