Hold option immediately upon startup and a screen will load with a picture of a System folder, a Next button and a Continue button. The option key at startup does not work with my Logitech keyboard (nor does any other startup function.) Also, my normal boot drive is connected to a PCI card, not the onboard ATA/IDE controller. So, that does not show up in the list of drives. (Though, that is only after PRAM zaps, which make the Mac "forget" where to find the drive. After booting from some other volume, the Mac finds the PCI card-connected drive with no problem. I'll have to see if, once found, the Mac can find that drive on an option startup.)