Gibovsky: You may end up being disappointed with your results (while the vehicle is moving), car speakers are specially designed with a bigger gap between the voice coil and the magnet compared to "normal" and / or "HI FI" speakers. What may happen over time is the vibration from the road / vehicle deflects the speaker cone (while playing music) so that the voice coil rubs on the pole piece of the magnet eventually rubbing away the insulation of the copper wire. You can hear the process as loud "graunchy" noises and eventually when the bare wire makes contact with the metal frame of the speaker to the car body you may get some "Lucas" smoke as well. However if your PC speakers are in self contained plastic boxes and not screwed into the body (electrically) then you will be spared the smoke bit but that speaker will stop working. You may be lucky also if they are the smaller size speakers with a stiffer cone (read cheap LO-FI) and do not deflect enough to rub the voice coil, then the above does not apply ... However enjoy your music.
