The really good news is that you can use a single payment to buy OS X Lion and install it on any of the computers that you have authorized with your Apple ID. That is not a bad deal at all considering that you can authorize up to five computers with a single account, making the total cost of each install about $6. Now, you could just download the installer on all of your machines, but that will take up plenty of your time, since each download (the OS X Lion is 4GB in size) could take up half a day. A better solution is to create a disk image so that you can install it over and over again without multiple downloads.
Download Lion
If you have not done so, you can go ahead to download the Lion installer from the Mac App Store. Remember, you only need to do this step once.
Once you have finished the download, do not run the installer! Once the installation start, you won’t be able to create the disk image.
Creating a portable disk image
Plug in your USB drive (or external hard drive). Make sure your USB drive has more than 4GB of free storage space. Now, go to the location where you downloaded the new operating system and copy the OS X Lion to the external drive.
This could take a few minutes to transfer over. Once the transfer is completed, you can unmount your USB drive from your machine.
Installing
Putting the new OS on your system will be pretty easy from here, but before you do that, it is best to backup your existing system. Go ahead to make a backup copy with your time machine. If you did not setup your time machine before, then you may want to do that now.
Once the backup is done, you can plug in your USB drive and begin the installation. Remember, the machine has to be authorized under the same account in order for this to work. Begin by dragging the installer package to the Applications folder of the new machine. Next, double click on it and the installation will begin.
Now, just follow the screen instructions to finish the install.
