DVD HU + Computer?

Hey, just a quick question about DVD/NAV head units. I am toying with the idea of getting one (after taxes come back it will be much more than toying) and a question popped into my mind. Do any of these head units come with an input that I could hook my laptop up to to clone the screen? Not necesarily a VGA but an S video as well. I am doubting the whole think because I would also have to hook up a audio input but I was wondering if any of you had any experiance with this.
Thanks

 

I'd imagine you ca do it, as at the very least you can get a S-Video to RCA adapter from Radio Shack. From there, you can get a headphone jack to RCA adapter, and then you'd have sound.

but the big question is, why do you want to take a 15" or better screen and make it display on a 4" or less screen?