To create a motion button:
Drag a movie to your iDVD menu. If the resulting button shows an image from your movie (instead of just text), go to step 3.
If the resulting movie button is a text button (which says either the name of your movie or Play Movie), click the button once to highlight it. Then click the Buttons button and select a button shape.
Click the button you just created. If the clip is playing in the button, select the Still Image checkbox that appears above the button (shown below).
This stops the motion on the button.
If you want to select a different starting frame for the movie, drag the Movie slider.
With your pointer over the menu, press Command-I to open the Menu Info window.
Drag the Loop Duration slider to the number of seconds you want the movie to loop (up to the length of the video clip or a maximum of 15 minutes if the clip is longer).
Click the Movie checkbox to turn motion back on for the button, and then click outside the button to deselect it.