Spear pillar, exclusive to Pokemon Diamond.
You cant catch diaglia or palkia. The only way is the arceus event. When it comes out you get to choose diaglia, palkia or Giratina. That sucks^
you can trade with someone that has a dialga in pokemon diamond
if you get arceus and go to the ruins and you can chouse between palkia, diaglia, giratina. SO YOU CAN CHOOSE GIRITINA OR IF YOU CHANGE YOUR MIND YOU COULD CHOOSE PALKIA OR DIALGA
if you get arcius and go to the ruins you can chouse betwien palkia, diaglia, girancha.i got palkia and arcius from pearl i am waiting for blackCheck out soul silver legendaries on serebii.net. I think you can, but it is very hard and it is after you get 16 badges and beat red who by the way has a level 88 pikachu or something.
You don't need any seeds. All you do is stock up on apples, some boost seeds, some strategic seeds and some reviver seeds. Once you get up to the temporal tower, you have to fight Dialga and win. Afterwards, it will join your team at level 47
You will need the 7th Gym Badge and go through Team Galactic's HQ in Veilstone City. When you encounter Cyrus at the top and stop him from extracting the red gems from Uxie, Azelf, and Mesprit. He'll, then, go to Mt. Coronet, where you'll need to go and reach the top to Spear Pillar. He'll summon Dialga after defeating his Commanders and Cyrus himself.