Hi there, the easiest way seems to be to go to
http://www.rapidshare.de/ Click on where it says Browse and point it to the MP3 you want to use and upload it.
When it is done you will get 2 links, 1 is to be used to post a link to the download and the other is used to erase your file off rapidshare when you don't want anyone to use it anymore. There are others m8 but rapidshare seems to let you upload larger files.
Good luck with your MP3