It seems like you still don't understand the very primitive concepts around game programming… I suggest you pay a visit to http://www.jmonkeyengine.com/wiki/doku.php, especially the flag rush tutorial.
Runescape, as ugly as it is, is a very deep and complex game and would take a while (and a lot of manpower) to clone. I also suggest getting more comfortable with the API, then take on a simpler challenge first.
Any ideas on a simpler challenge?