Although iMovie3 claims to import any Quicktime-compatible clip, the short MPEG clips taken by my camera aren't selectable through the input dialog.
Nevertheless, they can still be imported by dragging them to iMovie from the Finder. The catch is that the sound is lost in the process, despite all my attempts to save it. It ought to be simple enough to extract the sound from the MPEG and import it separately, though.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030205070752125