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.
you need a action replay
yes and you need regice registeel and regirock to get him in pearl dimond or platinum
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.
Dimond and Pearl Dimond and Pearl Dimond and Pearl Dimond and Pearl
you must trade for it, or migrate it from ruby/sapphire it is unobtainable in Pokemon diamond. it is in platinum, though. there you need to take the lvl. 100 regigigas from the 11th movei in Japan with you, and you will find there is a new cave accessible in mt coronet, and there the patterns on the floor look like regice's eyes, and then it appears. but of course that doesn;t matter :-)
You can get the three regis on ruby/saphire/emerald. Then migrate them onto dimond/pearl/platinum and go into the snowpoint temple to find regigigas.Make sure the regis are in your party. You must have national dex!
the hope dimond
Jack Dimond's birth name is Jack Harry Dimond.
Tony Dimond's birth name is Anthony Paul Dimond.
you need to have atleast beat the Pokemon league once in dimond and you should be able to migrate.You also need either emerald version, Sapphire version, or ruby version catch regice, regirock, registeel then migrate into dimond version
who killed charlotte Dimond
You catch regice