I think you can record the mp3 music as you play it on your computer. For this, I think you can use an IC like the ISD2532. and then use it in the doorbell that you wish to design.
A typical application circuit is available in the datasheet of ISD2532. Try going through it.
Hey is anyone interested in a project about TCP performance and enhancement mobile ad hoc networking (MANET). i bet you one thing it is an interesting topic to discuss