[header] How to boot a mac from usb drive [title] Download mac lion installer from app store. [step] Latest versions of mac are only available through app store. [title] The download can take some time depending on your internet connection.
[step] Don't worry if you lose connection halfway through download, it will resume as soon as you are re-connected to app store. [title] Make a backup of the installer you downloaded from app store and save it on your desktop.