You can set chapter markers in iMovie that are exported with your movie when you export it to iDVD. Follow these steps in your iMovie project:
1. Click iDVD in the Button Bar
2. Select a clip in the timeline viewer.
3. Drag the playhead in the timeline to the point where you want the chapter to start.
4. Click the Add Chapter button in the iDVD pane. Chapter markers appear in the Timeline as yellow diamonds.
5. Type a chapter title next to the thumbnail that appears in the iDVD pane. (The titles can be changed later.)
Repeat steps 2 through 5 for each chapter you want to add. You can continue to add up to 36 markers.
Note: The Time column will display how far into the iMovie each chapter begins. The first clip will always display Time 00:00:00.