Installed 10.5 on 800mhz Ibook w 1.12g memory and a 160G HD. Used the gray replacement DVD start up disc that I purchased through Apple for my macbook since I bought it w out discs. Had to do a terminal cpu speed bump go around, but it fully installed and updated. Tried usb hd boot drive and a install through macbook to ibook as an external firewire HD w no success. As a last ditch effort before I ran out and bought a firewire external drive i tried this method. http://www.lowendmac.com/osx/leopard/openfirmware.html Its not life changing fast, but i can back up iphone and install my new printer on it. Just thought I'd share this w people trying to squeeze some last breaths out of their old machines.