I purchased a MBP in 11/07. It has OS X 10.4.11. I was eligible to purchase a Leopard 10.5.1 upgrade disk and did so. Today, 10/5/07, I finally got around to attempting to use the disk. After choosing a language, I receive a message that my computer needs to have 10.4.x or higher for 10.5.1 to be installed and my computer does not have this operating system. Does anyone know what is happening?