To add a soundtrack to a menu:
Open the menu where you want to add or change the audio.
Use one of the following methods to add a song or playlist to the background, or to change the audio that’s already there.
Note: If you’ve already added a background movie that has sound to the menu, that sound becomes the soundtrack for the menu. Any audio you add using one of the following methods replaces the sound from the background movie.
Click the Media button to open the Media pane, and then click the Audio button. Now drag an audio file or playlist directly from the Audio pane to the background of your iDVD menu. You see a green circle with a plus sign when it’s ready to drop.
You can’t drag playlists directly from the iTunes application.
With your pointer over the menu, press Command-I to access the Menu Info window. Drag an audio file or playlist from the Audio pane, or a QuickTime movie from the Movies pane, to the audio well (shown below) in the window. iDVD uses only the first audio track in the QuickTime file and ignores the video.
Click the drop zone button at the bottom of the iDVD window. Now drag an audio file or playlist from the Audio pane, or a QuickTime movie from the Movies pane, to the Menu well in the drop zone editor.
Open the Menu Info window, if it is not already showing, by placing your pointer over the menu and pressing Command-I. Drag the Loop Duration slider to adjust how long you want the audio file to play.
The duration you choose applies to both the audio file and any background movie you’ve added to the menu. The maximum duration is the length of the longest piece of media (song, playlist, or movie) you have added to the menu, up to 15 minutes.
Adjust the volume of the sound by dragging the Menu Volume slider to the right or left.