Other options
You can also choose to use a circular saw or chainsaw to remove the wood slats from the rails of the pallet. This will yield shorter pieces of wood (about 18″ slats from a 42″ pallet), discarding all edges with screws. This is the fastest way, but you loose some wood. One important thing to remember when using chain saws or circular saws is to not let the chain or blade make contact with the nails. You could damage the saw or be injured by a flying shard of metal.
Pallet wood is rough and nails are dangerous, so no matter how you disassemble your pallets, be sure to wear safety glasses and work gloves. Before you start your project please read this article : Red Flags to Watch Out For When Choosing a Pallet For Craft Projects to insure your project lasts. 
Photo Courtesy of Evolution Fury