When you're planning a trip, everything works like clockwork. It's only when you hit the road -- or the sea or the air -- that it all goes to hell. Such adventures may make for great drama or great comedy, however, and Hollywood has made the most of them. Take "National Lampoon's Vacation" (1983), in which Chevy Chase takes his family to Walley World, only to have car problems, family problems and Walley World problems. Lesson: Don't let your mind wander, especially when you've tied a dog to the bumper.