To get Regirock you will first have to beat the game-you will also need a Pokemon with a water ability, two Pokemon with a break x3 ability, and a fire x3 ability.
Just before you go into the temple use break x3 on the rock to the right. Then use water on the plant. Climb it then use break x3 on the wall. Go inside. There will be some Gastlys(catch them if you want it doesn't matter). Then go to the end and use fire x3 on the ice block. Go inside the big doors and Regirock will be inside.
Added by: arbiter88 Jan 21st 2007, ID#2014