For now you cannot do it. You can have text appear later in menu if you use split cell, but it will just pop up, not scroll in. You could do it if you prepare your menu in Premier and use underline for button once the Mpeg is in DVD Lab menu.
Premier is Adobe software. I just checked Mediachance web site and they have Edit Studio Pro, much cheaper than Premier and I think it will do what you want. http://www.mediachance.com/video/index.html http://www.puremotion.com/editstudio/showcase/