DVD Studio Pro allows the menu buton of your DVD player to have various control depending on what area of the DVD you are navigating from. A common mistake is to set Menu1 up as a short first play movie, but leave the overall disc control of the menu button to go to that menu, causing the viewer to have to watch the first play movie every time the menu button is pressed.
In the Outiline of a DVD Studio Pro project, select the Disc icon (at the very top), which as long as you have saved your project, will display the project name. Once the Disc has been selected, move your attention to the inspector, specifically the menu button destination. In most cases you will want to route the control of this button to the main menu, but you can certainly select anything you want.