Here is a simple tutorial I wrote on how to insert custom music, for those of you who are struggling:
1. Download carol's addmusic here: http://www.smwcentral.net/download.php?id=166&type=tools
2. Download and apply this IPS patch to your ROM: http://bin.smwcentral.net/952
3. Download a song from SMWCentral here: http://www.smwcentral.net/?p=list&type=music.
4. Rename the .txt file from the music you downloaded 20.txt and put it in the "music" folder that came with addmusic. You can replace the "20" with any number from 20-FF.
5. Put your ROM in the same folder as addmusic.
6. Open addmusic.exe and type in the ROM name.
7. Open Lunar Magic and click on the note block button.
8. Under the "Music Bypass Setting" drop-down list, select "20 not used" (or whatever number you named it).
9. Test out the level, and it should work!
If you have any questions, just post a reply to this topic. If a moderator feels this tutorial is useful, please sticky it.