Just like with most other versions of OS X, 10.6 Snow Leopard can be installed from a USB drive which is especially beneficial if you’re a Macbook Air user…
Before you start make sure that you have enough space , Leopard is just a shy over 6.2Gigs, and that your USB drive is bootable.
- Using DiskUtility select the USB drive
- Format it as Mac OS Extended (Journaled.) Give it a sensible name in case you need it later
- Still in Disk Utility, use the restore option with source = DVD and destination = USB drive
- Start the restore and wait. Should be less than 15 minutes
- Connect the USB drive to the MAC and reboot / boot it holding the option/alt key down until you see a list of available volumes.
- Select the USB volume and install.