It is impossible to get both on the one game, except for the three ways I will tell you now.
The first (possibly, I don't know because I don't use AR) is to use an Action Replay code. And don't ask what it is, because, as I said, I don't use AR.
The second is to trade it from a friend, who has the other version of the game. Even if you offer, I doubt they will accept.
The third, and the way I got both on Pearl, is to use the GTS. First, I caught a Dragonair (http://Pokemon.marriland.com/diamond_pearl/pokedex/dragonairfor the location), Although it would be easier to catch a Dratini in the same place and evolve it. I traded that for a Garchomp, and that for Dialga. However, you may be able to trade said Garchomp for a Palkia instead. Some other Pokemon you may be able to trade for Palkia are Empoleon or Spiritomb. For Empoleon, you can breed an Empoleon with a Ditto (http://Pokemon.marriland.com/diamond_pearl/pokedex/ditto) and train the piplups up to empoleons. If you chose Piplup at the start, this is easy. If not, try speaking to a friend who did, or trade one of the GTS for something else. Spiritombs (http://Pokemon.marriland.com/diamond_pearl/pokedex/spiritomb) take quite a bit of patience to get. Use that guide to catch it, but don't trade it straight away, as you can breed it with said Ditto to get some little baby Spiritombs, and them you can trade for a LOT on the GTS. You don't even have to level them up.
Hope this helped, and sorry for making the third way so long
You cannot catch palkia in diamond and dialga in pearl but you can catch both of them in Pokemon platinum
You can only catch dialga in dimonid
You cant but get Pokemon platinum you can get both dialga and palkia
Palkia and Dialga do not evolve. Legendary Pokemon don't evolve. Palkia and Dialga are both legendary Pokemon that appeared in the game Pokemon Diamond, Pokemon Pearl, and Pokemon Platinum, so they do not evolve. By Allen306 That is wrong my friend palkia and dialga do evolve Palkia evolves into ducbag Dialga evolves into ashole
Its the Pokemon creators way of making you buy both Diamond and Pearl... so you can get Palkia and Dialga...
you get dialga in Pokemon diamond--and no, I caught both my game's fine...
They are both exactly the same except Diamond gets Dialga and Pearl gets Palkia.
They are both equivalent, with minor changes, such as Palikia in Pearl and Dialga in Diamond. The only thing that changes is the Pokemon that appear and what time.
if you want more Pokemon yes because different Pokemon appear in each game apart from dialga and palkia
Pokemon Diamond and Pokemon Pearl have, essentially the same basic game play. They both have the same story line and characters - in fact, the only thing that differs are the Legendary Pokemon (Diamond - dialga, Pearl - palkia) and a few other Pokemon However, out of the two title Legandaries, Dialga is thought of to be the best. Pokemon Diamond has also sold more copies than Pearl, suggesting the latter is worse. Most evidence suggests that Diamond is better.
No Pearl Is Better because palkia and dialga are the same put palkia has 1 bar more speed. Also because dialga has roar of time palkia has spaial rend roar of time does more damage but spacial rend does over half of roar of time and roar of time has to recharge
NO!!!!! YOU CAN ONLY CATCH PALKIA ON PEARL you can't catch dialga on Pokemon pearl but you CAN trade it you only get both in Pokemon platinum