Use the multimedia dock or car dock to change the orientation of the home screen. Otherwise the only things that switch to landscape are apps themselves when they require/support it. You could also try a magnet (similar to the ones on the docks) to force the Droid X to "think" it's in a dock and rotate the home screen. Not sure how powerful a magnet to use but you could tinker with it and see if you can get it to work.