Disable generating thumbnail in iMovie '09

How can you disable the automatic generating thumbnail feature of iMovie '09?

I went through the process of transferring all of my video files from my video camera (Sony Handycam HDR-SR7) to an external HD (G-Drive). Now, when I launch iMovie to transfer new video files, iMovie begins the generating thumbnail feature which I can't stop. At this point, I'm waiting ~3 hours before I can begin the transfer process for new files.