Buzz Lightyear is tearing around on his jetpack in Toy Story 2, but I'm notwatching passively. Every time he banks left, my chair banks left. When he accelerates and climbs, I tilt back. When he finally touches down on a strange planet, my seat drops with a bump. No, I'm not at a theme park or "4D"-equipped theater -- I'm sitting on a couch. Specifically, I'm at the Paris headquarters of Immersit, a company that wants to turn your trusty sofa into an honest-to-Dieu ride simulator. I got to take a spin on its latest prototype, and spoiler: It was pretty cool. But would anybody be willing to pay the price of a decent laptop to get 4D at home?