Does anybody have one that they use in their car as a second monitor to their "hardwired" A/V system? If so, is there a cable that you need in order to run the signal from your hardwired DVD player to the portable so you can see the picture, not necessarily hear the sound?

I got the idea after going to Best Buy this weekend and seeing how inexpensive the portable ones are right now. I'm sure it's been done, but I hadn't seen it discussed in here before.

Thanks in advance