Yeah, we all know you can't use it as a backup via Airport Extreme. However, I have my drive being used by my 2 computers. Here's how I did it: 1. Get it working on one of the computers. This should ideally be a stationary computer that the drive will never disconnect from. 2. Go to System Preferences>Sharing. Turn on File Sharing. 3. Click the + under the Shared Folders area. 4. Go add the external HDD. 5. Edit the settings to the right as necessary (you can determine what you want). 6. On another computer, go to the Finder. Go connect to the computer with the HDD attached to it. 6.5. Depending on what preferences you set, you may want to hit the Connect As button, then input the appropriate user. 7. Find the HDD. It will appear as a folder, not a hard drive symbol. 8. Open it up. You don't need to do anything with it. These steps were simply to make sure this computer can recognize the HDD. 9. Go to System Preferences>Time Machine>Select Disk (or Change Disk, or whatever). That remote disk should show up in the list. 10. Select that disk, then you should be good to go! I can't guarantee it will work that easily, but that's what I did and it works!