My 2002 has the factory-installed DVD in the overhead console. They offered an Audiovox unit that consists of a head unit below the 2nd row seat on the driver's side, and the flip-down screen in the overhead console.
The screen is pretty small (7 inches?) but on the plus side, I can still use my rearview mirror when it is down. People with the big 10 inch screens have noted that they can't use the rearview mirror at all when the screen is down.
When I bought mine I was surprised that I had to open the glove box, flip the FM Modulator switch, and then tune the FM stereo to 89.1 in order to hear the DVD over the stereo system. However, my kids like using the wireless headphones, so that's what we normally do so I can listen to the stereo while they watch movies.
I like the fact that they can change disks without bothering me, so I wouldn't want the head unit up front.