First I would like to see your video so as to understand what is your actual requirement. If the 2D animation is in Flash, then it will be very easy task to do it. Can also add your MP3 in it and final output can be given to you in any format like swf or exe or video (WMV, AVI, MPEG... etc)
Will submit you my 2D flash animation work if you like to see it for your satisfaction.
Awaiting your prompt and positive response.
Regards