okay heres what i have to say.
On the note of prequels... there are already prequels based on Jack Sparrow and his adventures battling off Captain Torrents, Hernando Cortez, Davy Jones, Madame Minuit, mermaid kingdoms, dinosaurs, sabretooths, Aztecs, etc. In that he actually hates pirates. I only read half the series, i think he changes his mind on pirates when Teague comes in "Sins of a Father", so i dont think that the pupeteer-pirate-atlantis thing is any close to being a good idea..... Another set of prequels is when he's an adult and a pirate lord, battling the Shadow Lord with the help of the Brethren court, so there is a time difference between the two series....... The first series should definitely be made a movie series....
And what Babidi said is somewhat wrong - the story of Davy Jones is complete, and if a movie were to be made about him, it should be only 3d animated like what happened to Clone Wars, as a film of DJ will not be getting much at the box office... Jolly Roger would also not be put in a movie though i feel he should.
Lastly, Pirates 4 is a sequel, and it is very much true that Johnny Depp and Brukheimer cant give up on a movie who's title has been made already....