2003 Intrepid CD/MP3 Troubles

Are you referring to an optional  factory external cd player unit?  And using the radio's input for that component, to hook up an mp3 player?  If so, I doubt you'll be successful as usually they use DIN plugs with the factory components.  Also, even if you managed to get a DIN cable to splice in to, the sound inputs would almost certainly not be compatible and you wouldn't be happy with the way it sounded.

As for the future, I don't think the manufacturers will offer stereos with those features any time soon.  Closest thing I've seen was for the 03 accord (and I'm sure many other vehicles by now) you can get an external CD player that mounts right in front of the gear shifter, and it is mp3 CD compatible.

They do make aftermarket decks with front-panel auxilliary inputs.  Aiwa and JVC and maybe some of the other brands offer this feature.  ( http://www.crutchfield.com/cgi-bin/S-GTiYeB7FXn7/ProdView.asp?s=0&c=3&g=62700&I=570CDCMA01&o=m&a=0&cc=01&avf=N).  And of course nearly all brands now let you get a special adapter cable to plug in to the stereo's cd changer connector, that lets you use that as an auxilliary source.

I would get a new after market head unit that plays cd,cd-r,cd-rw, and mp3 formats. Then you can burn cd's in mp3 and get 100 hrs a disc. aftermarket is always better than oem. or get a kenwood music keg that you can hook up to the factory head unit.