After you beat the seventh Gym, go to Spear Pillar (Google for a walkthrough on how to get there). After a few battles and Cyrus's ranting, Palkia will fully awaken and you will get a chance to catch him. Be warned: this is your only chance! Save before battling. I suggest confusing him right off the bat, getting his HP down just enough, maybe put him to sleep, and use a whole bunch of Ultra Balls.
Catch/Defeat PALKIA
To catch Palkia, you have to get a Lustrous Orb from Pokemon Pearl, and an Adamant Orb from Pokemon Diamond. Then you have to go to Temporial Tower. You will have to catch/defeat Dialga first, then catch Palkia.
uxie azelf mesprit and palkia
To catch palkia you will need to trade him with Pokemon pearl. NOTE: You catch palkia in pearl and dialga in diamond.
You can't catch Palkia in Pokemon Diamond, you'll have to trade with Pokemon Pearl
NO
Palkia
You cannot catch palkia in pokemon diamond!
Palkia, Arcuise, Darkrai, Cresselia, Shaymin, Mesperit, Uxie, Azelf, Regigas, and Heatran.
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
You cannot catch Palkia in Pokemon Black and White you much use Poke Transfer on Route 15
You cannot catch palkia in diamond and dialga in pearl but you can catch both of them in Pokemon platinum