iMovie '09 brings back the capability to speed up or slow down clips, which went missing in iMovie '08. Select a clip and bring up the Clip Inspector by double-clicking the clip, clicking the Inspector button on the toolbar, or pressing the I key. Just as with its last appearance in iMovie HD 6, you can move a slider to make the video play back slower or faster (indicated by a turtle or hare icon).
You can also enter a value into the text field to the right of the slider, and this is where things get interesting. You're not limited to the tick mark values on the slider, so you can set the speed to be 118% of normal if you want. The field below that tells you the clip's changed duration.
But you can also exceed the boundaries of the speed slider. Enter any number between 5% and 2000%, then click Done.
From Jeff Carlson