you need a action replay
You can only catch it in Ruby, Sapphire or Emerald and migrate it over. If you get an event Regigigas on Pokemon Platinum you can catch Regice there.
Dialga
i know you can catch a ditto
you catch one
luck
no you can, you most catch it in Pokemon emerald
pee wee Herman
go to the mansion garden
There is no possible way to catch Regice in Black or White, unless you use PokeTransfer or Dream World.
You can't... without Action Replay. I do not know a legit way to get Regice (along with Registeel and Regirock) The only Regi I know how to get legit is Regigigas, which needs Regirock Regice and Registeel. If you know a legit way to get Regirock Regice and Registeel, edit this answer. actually you can. all you have to do is send Pokemon from ruby, or Sapphire to dimond or pearl or platinum. then trade it to soul silver.
you have to trade from diamond or pearl
in island cave idiot