yes you can also catch them in soul silver.
no
no.
try to catch your legendary. It varies on which legendary depending on what starter you chose.
You don't, the three 'crown' Legendary Beasts are obtained via a wi-fi event for SoulSilver/HeartGold.
Trade them from HeartGold and SoulSilver.
a utra ball or a master ball
If by enti you mean Entei the legendary dog then yes, all three dogs are there.
you have to catch Palkia(in pearl)orDialga(in diamond)
grovile
You are stronger of cource by pecy Jackson
Strong Pokemon like lugia, ho-oh and the three legendary dogs
After you catch them like any Pokemon they are saved on your pokedex and ready for use.