Will you be able to catch Dialga or Palkia on Pokemon platinum?

yea you can all you have to do is get your national dex and beat the elite four then go to the cave where the drawing is in celestic town the Cynthia will come and she will start talkin. but listen to everything she say. then go to mt coronet and you know where you caught giratina it will be a blue portal to dialga and when you catch it, go out of the spear pillar and go back in and you will see a red portal to palkia. i hope this help you.