Instructions
Connect your "Pokemon Soul Silver" cartridge to the Action Replay and place the Action Replay into the Nintendo DS's cartridge slot.
Turn the DS on and enter the "shiny" code at the Action Replay's code screen. Press "Start" to continue.
Select your save file and press the "A" button.
Press and hold the "R" and "L" buttons to activate the "shiny" code. Once you have activated the code, all Pokemon in your party will be shiny.