You gotta live an easter egg that features nudity :)
From the discís main menu, select 'Extras' to get to the submenu of special features. Here, highlight the 'Main Menu' entry and then press the 'Right' arrow key on your remote control. This will highlight a circle. If you press 'Enter' now, the circle will turn into an opening reptilian eye, which takes you to alternate takes of scenes from the movie (featuring some Tanya Roberts nudity).