Yes, to catch Giritina, Cresselia, and Mesprit. In Pokemon Platinum, you can catch Zapdos, Moltres, and Articuno also. :)
catch legendary Pokemon like giratina and heatran
You have to defeat the elite four then you can catch the legendary
Beat the elite four. Catch the legendary pokemon, Giratina. after that you can just roam around but that's the end.
defeat all gyms,elite 4 and champion of that region to catch legendary pokemon
you can't catch it because you already beaten the legendary
You can't catch Dialga in Pokemon White. After you beat the the Elite 4, you can use the PokeTransfer to receive a Dialga from Pokemon Diamond, or Platnium.
no
you can start over
5
Yes quite a lot of them
Kyogre only.
there is no best spot