I would assume that an in-car LCD would have composite video input.
Meaning, you would need something like this:
http://www.electronicsoutfitter.com/store/gez-1000.html
That would convert the VGA from the x50v to a composite video signal for the car monitor.
Looks to me like that gadget draws it's power from the USB port, so you'd need to splice it into your x50v car charger (if you have one), or buy a cigarette -> USB charger for it to plug into.
Once you have that setup, you'll need a VGA cable for the x50v.
PC Mobile sells one for a good price, as does a duder named chrismax (I think) on these forums.
Then, plug VGA cable into x50v, VGA cable into convertor, convertor into car LCD, and convertor into USB charger. Voila.