It should be fairly easy to unstick this one. Check the valves as they have a tendency to stick. Whatever you do, DO NOT pull it to get it unstuck. Expensive parts can be damaged or broken doing this. I recommend PB Blaster (available at Wal-Mart) and Kroil (www.kanolabs.com) as the penetrating oils of choice. Some folks like Marvel Mystery Oil and others swear by diesel fuel.
First, remove all the sparkplugs and check for water in the cylinders. Remove any water and fill each cylinder with your penetrant of choice, then reinstall the plugs. Now, let it sit for a week. After a week, remove the starter and use a pry bar on the ring gear to try and turn the engine. If it doesen't move, wait another week. Time is your friend here. Repeat the process until the engine starts to move. Rock the engine back and forth until you can get a full turn of the crank.
If there is no success with the cylinders, check the valves to see that each one will move. Use a pry bar to depress each valve in turn. Apply penetrant to any that do not move, wait a week and try again. Keep working on them until they all move.
Basically this job is simple patience and lots of elbow grease.