With Aperture 1.5’s ability to import files as references, you can easily keep your images on a portable, external drive. If you regularly move between a laptop and desktop computer, this is the easiest way to quickly move data back and forth - just move the drive between computers.
For more thorough portability, though, you might want to consider placing your Aperture library on the same external drive that you’re keeping your external images on. Simply go to Aperture’s Preferences and click the Choose button beneath the Library Location field. In the resulting dialog box, select your external drive.
Now Quit Aperture. If you restart, you will see an empty library, because Aperture is pointed at your new library, which hasn’t yet had any images imported into it. If you’d prefer to work with your old library, copy the Aperture Library.aplibrary file from its old location (by default, this file will be in your Pictures folder) to the new location that you specified. When you launch Aperture, you’ll see your library, just as you’d left it, but it will now be stored on the external drive.
Plug the external drive into your other Macs and configure those copies of Aperture to point to the library stored on the external drive.
Now, whether you import images into the Aperture library, or import them as references to files stored on the external drive, you’ll be able to move the drive from computer and work with the same library. And, of course, your referenced files will be easily accessible from other applications. Remember, though: referenced files are not backed up using Aperture’s Vault system.