I'm not sure I would recommend rushing right out to a theme park on your day of arrival in any event. While a WDW vacation can indeed be quite hectic, it should really be rather relaxing. Take that first day to get settled in at your resort, maybe lounge around the pool or rent a speedboat. Try some time at DisneyQuest or strolling around the rest of Downtown Disney. The suggestion to head to EPCOT for the late afternoon/evening is an excellent one--have a nice dinner in one of the World Showcase restaurants, mosey around the lagoon, and enjoy Illuminations.