were it me, I'd go iPod. The Zune is failing miserably by all the sales statistics from the beginning of the holiday season until now. I'd be worried support for it is going to disappear as far as content (movies, music, etc.)
The iPod has proven itself to have longevity and continuous bacwards support back to the first model. Just my .02
Oh, and you will find a lot more aftermarket support in the way of accessories and aux inputs beyond just line-in.
_________________
2008 Unlimited Rubicon - 3.5" AEV/Nth lift - 35" MT/R with Kevlar - AEV Wheels - York OBA
2008 Patriot - Fuel Saver
