OK, Getting Serious,
You've got to have the MP3 files on the card,then put it in your
Wii's SD slot on the front.
Then make sure that you check the Wii Shop Channel that Photo Channel 1.1
has not been downloaded since it can only play aiff files.
If you have it, go to the screen before Wii Settings and choose the one on the left
and go to the Channels tab and delete it.
Go back to the menu and choose the normal Photo channel.
Go to the Slide Show and press A then choose music
and that's it.