[JohnBoucher]

I would always ask to use some ones music. The only artist that I know of that ever released their music into the public domain was the Grateful Dead, and they were specific that you could not profit from it.
Asking is the easy part. Explain about FIRST and your team and how cool it'll be to associate with the program. Tell them how you will use the music and for how long you will use it.
Make sure to acknowledge them on your website.

BUT......

Check your download times. Music can really slow down a site. It is best to code for dial-up.
Have some way for your users to turn off the music if they want to.

Personally, I surf with the sound off.

$0.02