Instructions
Insert the SD card into the PC.
Click "Computer" or "My Computer" to open Windows Explorer. Click the SD card from the list of drives.
Create a folder on the SD card for each playlist you want to create. If you want just one playlist for all of your songs, make just one folder.
Drag and drop the music files you want to play on the DSi into the appropriate folder. Place the songs in the order you wish them to playback.
Remove the SD card from the PC and insert the card into the DSi. You can rearrange the songs using the stylus. The DSi has different playback modes. You can play the songs in each folder in order or randomly. There is an option to play a section of the song lineup.