To make duck or goose stock, you can pretty much follow the directions for poultry stock, but there is one major difference: Waterfowl had a lot more fat than your average bird, since they spend so much time mucking about in freezing water. Geese can live quite happily at temperatures down to -30ºF, and ducks can take almost as much as long as they have open water to swim on. So the trick here is to use just a little bit more water than the regular poultry recipe, and as your stock simmers, you'll notice that the top will be covered with a layer of melted fat.
Take a ladle and remove as much of the fat as you can from the top of the stock. You can simplify the process by using a gravy separator. Do what you will with the stock, but save that fat! Duck fat is delicious, and goose fat might as well be gold. I will never make a pie crust without it! And have you ever had a grilled cheese fried with goose fat instead of butter? OMG Nom!
Now, don't get me wrong - it's terribly bad for you. But it's so good. Just use it sparingly. (We usually eat about two geese per year, and get about 1½-2 cups of fat from each one, and we make it last until the next goose comes along.)