What you'll need:

• A compatible SD Card or SDHC Card. The Nintendo DSi is compatible with SD cards up to 2 GB and SDHC cards up to 32 GB.
• Compatible music files stored on a PC or Mac.
• An SD Card slot on the PC or Mac, or an SD Card reader/writer.

What to Do:

• Insert the SD card into the PC or Mac
• Open Windows Explorer (for PC) or Finder (for Mac) and select the drive being used by the SD Card to open it.
• Open another instance of Windows Explorer or Finder and navigate to where the music is stored.
• Highlight the desired file(s) and/or folders, copy them, and then paste them into the first instance of Windows Explorer or Finder to create copies on the SD Card.