After you’ve made your last edit, quit iMovie, and open a Finder window. Navigate to the Home folder (featuring your user name and a small house icon), and open the “Movies” folder. This should contain two folders: “iMovie Projects” and “iMovie Events”. These contain most of the information that iMovie is referencing when you work on an iMovie project.
Copy these two folders to your flash drive/network space.
When you log in to the next computer where you’ll be editing, Navigate to: Home>Movies and then copy the “iMovie Projects” and “iMovie Events” folders into this location.
When you open iMovie 09 your projects and events should be there, ready to go.
One thing to note is that sometimes we’ve had patrons lose the audio files they used in their projects during the moving process. If you know you’re going to be editing on multiple computers it might be worth trying to place your audio files in the “Movies” folder before you import them into your iMovie project in the first place, and then copy them, along with the “iMovie Projects” and “iMovie Events” folders.
More info with slides here: http://www.maclife.com/article/howtos/how_move_your_imovie_projects_around#slide-0