What You'll Need:
> Super Mario 64 DS
> A Nintendo DS, DSi, or 3DS (recommended you don't use a 3DS, though)
> An Action Replay (version depends on what DS you use)
Insert your Action Replay into your DS, and place SM64DS in the slot on the top of the Action Replay.
Plug the Action Replay into your PC using the USB attachment cord that comes with the Action Replay. Make sure you have the official code loader downloaded from the Action Replay website.
Find the SM64DS folder, and create a new code.
Look the code up on YouTube or Neoseeker, because KW isn't allowing me to post it. Darn numbers...
NOTE: For this code to work, you have to hold the SELECT button while selecting a file.