Well I have spent a lot of time researching and I'm one step away from being a very Happy Camper. I have gotten my retail OS X (10.5.4) loaded and have gotten up to where I need to do the 10.5.7 upgrade and that is where I have been stuck for hours. As noted pre 10.5.5 versions have a problem opening .dmg files. In one tutorial it suggests 'extracting' to an external drive and loading that way - HOW DO YOU EXTRACT A .dmg file???? I'm that close. Any suggestions will be most appreciated.