Car radio

Is it possible to take an old car radio and use it's amplifier with some other devices. Such as: MP3 player, pocket radio, computer and others.
I don't know much about amplifiers. So with what should I power the AMP.
Maybe someone could give me an circuit or something.

Input the signal to the top and bottom of the radio's volume control. You don't get much gain, though, but the power output is decent.