You are in luck, as many aftermarket stereo head units include an auxiliary input right on the front panel. All you will need is a 1/8th inch male to male adaptor cable to hook your MP3 player up to the head unit. Of course, you won't be able to control your MP3 player from the head unit--it will only amplify the audio coming from your MP3 player. You will need to use your MP3 player to select songs and control playback. Many Aiwa units include an auxiliary input.