I copied an iso for Tiger (legal copy) onto my PB's HDD and double-clicked the img file, at which point the computer mounted the image automatically. I could access the mounted drive and see it on my Desktop. When I clicked the "Install Mac OS X" icon, it told me to reboot for the installation of the new OS to begin. However, at startup it powers on as normal without the supposed installation. Also noteworthy is that the mounted drive disappears when the computer reboots. I've tried changing the file extension to .cdr, .dmg, and even .img, and holding down C and option to no avail. Am I doing something wrong? Do I HAVE to have a CD to install the OS or can I use a mounted img? Thanks for reading guys!