If you add a track from an audio CD into your iMovie HD project, you may be unable to eject that CD while iMovie HD is running.
This can happen if you’re using iMovie HD in Mac OS X 10.4 Tiger.
To eject your CD, save your project and quit iMovie HD. You will then be able to eject your CD normally. After the CD is ejected, open iMovie again and resume work on your project.
If you have a number of CD tracks that you wish to add to an iMovie project, you can avoid this issue by first importing the tracks into iTunes. Once they are in your iTunes Library, they will be available for use in iMovie HD without needing to have the CD in your computer.