you need REGIROCK, REGICE, AND REGISTEEL.
You don't. You can only catch Regigigas in Diamond, Pearl, and Platinum.
in the snowpoint temple
that doesnt make sense
You have to have a special Regigigas from an event.
you need event regigigas
No; you cannot catch the three Regis in Platinum, UNLESS you have obtained a special Regigigas through some special events.
only with a hacking device.
Fight the elite 4 and just train your Pokemon
Trade with Pokemon Platinum, Pearl, or Diamond.
I'm sorry but you only have one chance to catch him
You need a event Toys R Us Regigigas.
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.