You’ve probably seen the article about the Asus Eee PC and what can be integrated inside it’s case. But after you’ve done some modding and added different devices your battery probably doesn’t last as it was intended to last, so if you need to charge it in the car you either buy a commercial adapter or you make it.
This projects shows details on how to build an Eee Pc car charger. There are actually a small number of parts so the whole cost should be small.
ASUS Eee Pc Car Charger: [Link]