In wordpress, users can link to mp3s. When they do this I would like a small music icon to appear automatically before the text in the hyperlink.
It would look something like this:

<a href="link.mp3"><img src="http://auto-image.jpg" /> name of file</a>
The user would just create the link and the php would insert the image automatically.
I need a piece of code that would search the document for any links pointing to mp3s, then when it finds one it would insert the image.
I have no clue how to do this. Im a graphic artist who's way out of his league when messing with php. I'd be very happy with anyone who could at least give me a good clue.