I have been stymied in my attempts to use the install disks from a 20 inch Imac to install Leopard onto my trusty old 12 inch Ibook G4 1.2 ghz with 768 mb ram and a 160 gb hard drive. The installation ...

But then when attempting to retry the installation, the Mac App Store allegedly says that Lion is already "Installed," forcing them to launch the actual installer from the system's Applications folder ...