While I will be adding it on my '99 Chevy Suburban, it can very easily be done on almost all cars, SUVs, and trucks.
Many of you will notice that I have a cassette player as well as a working radio in the car so an FM transmitter or cassette tape with a headphone jack might be the more logical answer. I have actually tried both, and while they both work OK the inconsistency and lower quality of the FM transmitter and the reliability and constant cleaning required of cassette player if you listen to your ipod more than a few times a month just don't cut it when you can have a high quality maintenance free direct line-in for a little bit more.
I found the auxiliary input I wanted at
then bought it off ebay.
The basic tools required are:
regular crescent wrench
Flat head screwdriver
Drill and bits (I used a 1/4" and a 5/8" bit)
You'll also need a stereo mini (1/8") jack-to-RCA cord about 3 to 6ft long (depending on whether the folks in the back seat want to play with the iPod/mp3 player while your listening). This cord will be what connects to your music player.
Step 1: Preparing the car
If you have two batteries like me (it's a diesel :-)) you should disconnect both of them. Later on I also had to move my shift lever since it's attached to the steering column so I set the emergency brake too.