IMO,
1. the DVD changer is a FAR better option than the iPod option. I have hundreds of tracks that I've recorded onto the six DVDs. I never use my iPod or my iPhone to play music.
2. look at Invision for head-rest DVD options. They posted recently with some good prices.
3. there are recent threads on installing a "backup camera". You can search for that string.
4. don't bother with the iPhone 3G adapter (if you're thinking of adding that). I added that and it cost way too much, was way too much trouble, and I never use it.