If you mean with the 3 legendaries, the legendary bird pokémon Articuno, Zapdos and Moltres: you can't catch them in Diamond. You can migrate or trade them, since they will be roaming Sinnoh in Platinum. You can also find them in FireRed/LeafGreen, HeartGold/SoulSilver and X/Y.
You can not catch any of them in black or white, but I think that you can catch all 3 in diamond.
Actually I mean I can't get them cause we need 3 level10 Pokemon to get to them and then we can't catch them cause we can only have 3 Pokemon total. Then how are we suposed to catch them?!
Not necessarily, most Pokemon with a catch rate 3 are legendaries, making them very difficult to maintain but usually have very good base stats.
no, you have to trade w/ GTS
not. you will have to migrate them from emerald
catch palkia (pearl) catch dialga (diamond)
You can catch on at the Snowpoint Temple. However, you must have the 3 Regis in your party.
1.eat pie 2.Watch tv 3.USE A POKEBALL
Most legendary Pokemon (with some exceptions - mascot legendaries, in recent games, tend to be easier than other legendary Pokemon to catch due to being necessary to catch in order to advance the story), along with Beldum, Metang, and Metagross. These Pokemon have a catch rate of 3, the lowest catch rate in the games.
You can catch legendaries in any Pokemon game! (At least after you know where they're hiding!)
You go to the three caves and catch them.
After you've caught the main legendary( either dialge or palkia) there will be the three legendaries in the lakes- azelf, mesprit and uxie. :-)