I would not bother with and overhead screen.  I had one in my ML (an aftermarket Sony), and while it worked well, it was a PITA.  When open, it blocked my view, and whenever my wife went to reach into the back seat to deal with the granddaughter, she’d smack it.  It also took me quite a bit of work the get it to not rattle.

I would strongly suggest headrest mounted screens.  You don’t even have to replace or cut the headrests; there are some pretty decent mounting brackets you can buy that attach to the headrest stanchions.  Another alternative is to use a floor-mounted gooseneck and place the screen behind the center console (mimicking the VES setup in the W164).

As for the DVD player itself, get one that a screen and player combo.  I bought one from an eBay seller that has an 8-inch screen plus it has a built-in Nintendo 8-bit game emulator and a disc with 300 games.  I’m going to use a headrest bracket to install it in the new BMW X3 (it’s headrests are too small for built-in monitors).

C-ROD ... the problem is doing it for the first time ..... should be about 5 hours for MB ......

I took 6 hours !..... If I had to do it again 3 hours!......  The instructions say to take the headliner out (total bullshit) . YOu only need to take off  the passenger side top pieces (rubber seal, handles, inside light) .... then run the cable from behind the front passenger side glovebox, up the A-Pillar, under the headliner alongside the edge of the door opening to the pillar , then feed it though to the hole you cut behind the sunroof.

The point is if someone already did it in your area ... you would be in business in MAX 4 hours!......

THis might help, too:  http://mercedesml.info/sunroof/index.htm 

maybe we should post a the plate to show that the slits should be used to mark the outside perimiter of the hole , and not the size of the plate.

... let's see if I can find a big enough pic!....

I put a portable in the X3.  Because of the giant sunroof, a ceiling mount was not an option.  BMW offers their headrest mounted dual screen system for about $2K plus dealer installation, but the DVD player takes up the entire center console storage bin.  I looked at aftermarket headrest screen, but they all omit the headrest tilt feature, which I cannot give up.

I bought this:

DVD PLAYER ON EBAY  

And then this:

HEADREST MOUNTING BRACKET

The bracket is made for a universal slide mount LCD screen, but the “slide” part screws off to reveal a threaded post (like a standard threaded tripod mount for a camera).  It was slightly larger than the mounting hole on the back of the DVD player, so I used a tap to enlarge it.  The player is heavy enough that its bottom edge needs to rest gently on the seatback to stabilize it, but otherwise, it’s a great setup, and easily removable for storage or use in other vehicles.  It looks more professional than those strap-on screens, too.