Unfortunately, it is my understanding that Publisher does not support mp3
files as a background sound.
One workaround is to upload the mp3 file to your site, and then link to it
from your web page. You could introduce it, and invite them to download the
file and listen to it, by clicking on the link. I always tell people how big
the file is, which would be important to people with dial-up connections.
The advantage of this approach would be downloading the file would be
optional, and your web page will load much more quickly. People like fast
loading pages...
Here is a good article to read: "Including external files in a Publisher
web":
http://msmvps.com/blogs/dbartosik/archive/2006/01/07/80561.aspx
I know that if you download a pfd file, and have the reader installed, the
file will open automatically in IE. You might want to test to see if a mp3
file opens and plays automatically.
DavidF