Extension:Mp3Handler

Once you have installed this extension, you can upload Mp3 files in the same manner as images. To display them on a page, use the syntax, just like for images.

Note: Dewplayer is not free software, though it is free of charge.

Install and configuration
If you want to make sure that "download" really does download instead of playing in the browser, you should configure your server to set the MIME type to. Overriding  can make this easier.