Well make sure you are old enough to drive first, and hehn make sure oyu have a license and have passed a driving test to obtain it, in which case you'll be familiar with the rules and laws/regulations on these kidns of things.
I'm pretty sure removing your rear view mirror is illegal. And I'm also pretty sure I use it allot. There are these things called blindspots, you can't see them form your side mirrors, which is why we look in to the rear view mirror and hte side mirror before changing lanes.
They do make replacement mirros with tiny screens on one side of them, for backup camera's, but as I said above, repalcing the mirror with a camera completely isn't legal, nor sane, err, I mean, safe. Mirrors reflect light, so when oyur head moves, so does the image on the mirror, for better visability. A camera would thus have it's own blindspots, and is only useful for backing up, as not to slam into another object, if you need a camera to help with that (or jsut for cool factor ^^).
If oyu mess up your resolution or use a crappy VGA extension cable the picture on the Xenarc will get messed up. Jsut don't do either of those htings. Resolution is good at 800x600 or 800x400 (use PowerStrip if oyu video card supports it).
There is no way to make media engine take up half of the screen, or to split the screen on the xenarc half VGA and half video input.
If you get pulled over, just turn off your monitor. My monitor is mounted right above my radio, it's not obstructing my view of the road at all - non the less, it is illegal in most states ot have a monitor in view of the drive that is not used exclusively for GPS, so when getting pulled over, turn it off. Unless the cop pulled you over because of the monitor you should be ok. I've never had a cop mention it or any of the other crap all over my car (not even my purple LED's :P) when being pulled over.
Now, if you have removed your rear view mirror in place for a monitor, and are fidgiting with it when you get stopped, then I don't think you'll have the same luck . Do not remove or mess with your seatbelts, turn signals, headlights, or airbags either, in case oyu were thinking of doing so :P. And stay away from my car please.