How do you Acreus on Pokemon DiamondPearl?

the only way (i think) is by cheating to get the azure Flute. But if you have it go to the top of spear pillar and go up the stairs. As of now only an a cheat that gets you a flute. You go to Spear Piller and play the flute. Then a Staircase apears and at the top is a wild Acreus. A battle starts and you can catch the legendary pokemon.