There is already a thread identical to this : http://www.wiichat.com/nintendo-wii-...confirmed.html
November 10, 2006 - Over the last few days there's been substantial buzz around the possibility of the Nintendo Wii to allow for custom soundtracks for players via the system's SD card slot. Seen during the Nintendo Fusion Tour, gamers had been reporting that an option in Excite Truck allowed for users to implement their own music, though whenever attempting to enter the option screen they were promptly interrupted by Nintendo reps. Now that we have the final boxed copy of the game in hand, however, there's nothing holding the secret back. Excite Truck utilizes music customization.
The following is taken directly from the final Excite Truck instruction booklet:
Excite Truck allows you to listen to your personal MP3 music files during the game. By inserting an SD Card into your Wii console, you can choose the music you want to hear.
How to Select Music Tracks
1. Insert your SD Card into the Wii console.
2. Begin or continue a game and enter any race. Before the race begins, press + on the Wii Remote to access the Sound Options screen.
3. Select the "SD Card" option.
4. Any MP3 files available on your SD Card will be displayed (100 songs maximum). To choose a specific song for the race you are about to enter, highlight that song. You can also choose to randomize all songs shown for that course. Highlighting "Default" will play the standard in-game music.
5. Press 1 to return to the Sound Options menu, then 1 again to return to the pre-race screen. You can also use the "Sound" command at any point during the race to change the current song.
No word has been given if any other Wii titles will be implementing music customization, though if Excite Truck is any indication, expect to see the option included in future first party Nintendo titles. More as it develops.