dialga and palkia

Well, to start, you have to beat the Elite Four and Champion. Now, once that's over and done with, go back to Mt. Coronet. Follow the same path you took to chase down Cyrus, and find the area with the waterfall. My belief is that you climb the waterfall, grab the Adamant and Lustrous Orbs, the continue the climb. Once you reach the peak, SAVE!! You should see two portals, one blue, one pink. You take it from here.

NOTE: I have never gotten to this part as I got the game only recently, but that is my best guess.

You have to beat the elite four firts

You go in mt. Corrent and find a place with a waterfall the you use HM waterfall.(you get waterfall before you fight the elite four. Yes this means you have to defeat the elite four first.) Then you go in the cave at the top of the waterfall. You take One orb or the other.(I reconmend this because you may have to fight them both at once. You can do this again with the other one to so you CAN catch both. Then you go to the spear pillar and dialga (or palkia depending on which orb you took.) Then I think you either fight him at the spear pillar or you may randomly run in to him in tall grass. For more go to www.pokemon.com.