Peter, I have used a pulley system many times for docking boats, and my kids 15' Whaler is currently berthed this way. A pulley system is great for protected areas, but not the best system if the boat will be subject to high winds or strong current.
You will need to visit a local NJ Shore hardware store, or marine supply store for:
-4 large galvanized pulleys with swivel eyes on the end, and pulley wheels capable of holding 1/2" dia. rope
-4 threaded J hooks at least 1/2" dia. to drive into each piling for holding the pulleys. The hooks are threaded on one end to drive into the piling, (assuming they are wood), and open ended on the other to slip the pulley eye onto. Drive the J hooks into the piling, usually near the top to allow for flood tide. Best bet is to take a look at the other boats in your marina for the height required.
-4 heavy sash weights. This is a the tricky part. The weights need to be heavy enough to hold the boat steady in a storm, but not so heavy that it pulls your cleats out
Some buy actual sash weights from a marine supply. I've also seen home-made one from large Sam's Club pretzel plastic tubs filled with cement, and a galvanized eye hook imbedded in the cement.
-4 lengths of 3 strand dock line, 1/2" dia. with a spliced end. You will need to allow enough line for the boat and sash weights to go up and down with the tide. However, be careful not to make the ropes too long and have them resting on the bottom in a high tide. Tie the unspliced end to the weights, the spliced end to the cleats on the boat.
-you may need to buy an additional line for a spring line.
I would highly recommend you go to the dock first to see what you are dealing with, and also look at how others have tied up. Once you get the lines set, you should remain in the area and watch the boat fun through a full high/low tide cycle, adjusting the lines as necessary. Again, this is not the ideal set up for rough water areas. Good luck.