Go back to your NLE and add the text for the buttons at the 19th second on top of the background video that you already have. save a single frame as an image to use later. Export the footage as MPEG2.
Open the single frame in Photoshop as a background. Add a single layer and on that create the shapes that you want to appear adjacent to the text for the buttons to indicate the selection state. Now hide or delete the background, leaving just a white image with the underline, box, or whatever in place. Save that as a .pict.
Import the MPEG2 footage and the overlay file into DVDSP. Set the footage as the menu background and look in the property inspector. Adjust the loop point to be at 19 seconds and a few frames in to the menu. Once done, add the overlay to the menu and set it as the overlay. Draw out your button rectangles and set the button targets and navigation between the buttons.
What should happen is the first 19 seconds will ply, the text for the buttons will appear and the buttons will be 'active' after that. At the end of the menu, it will loop back to the 19 second marker and play from there.
it would be wise to ensure at least 30 seconds of footage exists after the 19 second point in order to avoid too many loops happening before the user has time to make their selection.