Only Allow Certian Attachment File Type

I’m in a bit of a pickle at the moment, and to be honest it sucks. 🙁 A huge element / factor I need to get working for this site I’m making is making it so you can only upload one attachment file type… .mp3 So if you try to upload a .jpg .png .mp4 or anything like that, it will simply not work and give you a generic error message. The only file type that should only be allowed in an attachement upload should be a .mp3 file… If anyone could help me to get this working, it would honestly mean so so much to me! 🙂

http://wordpress.org/extend/plugins/wp-user-frontend/