ahem.
Movies are filmed at 1.85 to 1, widescreen tv is 1.78 to 1, NTSC (tv) is 1.33 to 1.
the bigger the difference, the more you have to squish a wider image down so it fits. a movie viewed on a widescreen tv will fill the entire horizantal area, and have small bars on top and bottom. if you do the same hting with old tv, you have a lot more space on top and bottom, so much so that most people will view a dvd in fullscreen. what they may not realize is they are losing out on content by doing so. in order to convert a video from widescreen to fullscreen, the studio will crop the image on the sides so that it fills the entire screen image, but that means you lose content.
here are two pictures from wikipedia comparing the same image between wide and full screens.
Regular TV (4:3), aka Fullscreen:
Widescreen TV (16:9)
See the difference, all that image on the sides gets cropped off. Thankfully most tv shows that are filmed in HD dont crop the image down when you see it on a non hd channel, CSI for example is widescreen regardless of channel and tv screen size.