If you new HU doesn't have an aux-in (which it might on the back), just get an FM Modulator. You'll just tune to a certain FM frequency to listen to your iPod.
1999 Ford Contour SVT #900/2760 (SOLD)
2005 Mazda 6s
2003.5 Mazdaspeed Protege
1998 Ford Ranger 4x4