That's the trick. You need to convert your QuickTime movies into DV Stream format before you can import them into iMovie. To do this, you purchase QuickTime Pro. If you already have QuickTime Pro, open up your movie, select Export from the file menu, and select DV Stream as the file type. Then you can import it. Once you import the new file, you'll get a funky message, but just click "OK." The movie will be stored on your Movie Shelf.
To confirm, when I was using iMovie, this is how I did it. I don't know about the funky message but converting to DV let me import the file.
You just have to remember that iMovie is designed for the average consumer that wants to make movies from their home video camera most of which don't even know what DV or MOV is.