Do you own the original song and plan to upload it to your server or are you going to link to a song hosted somewhere else? Are you going to offer users to listen and/or download? How many songs are you planning to use?
I bought the song, and plan to be using it as background music in the website (client wants it, not me). There will be a small music player on/off control, but thats it. People won't be able to download it.
The safest thing to do is to contact the owner of the song and see if you can use it. If your site is a non-profit, you might get permission. Can't hurt to try!
