Welcome Mihai88ro. If you update your profile (location), then members may be able to answer as the options, etc. is different in different continents. Some older Euro-spec COMAND (as long as the software has not been updated) may be able to do this.
Yeah Eddy's right 05-06 models have the Engineering Menu available as long the software has not been updated, from this menu you can enable another hidden display and shut down / change the lockout triggers.
Whenever your car is put on the dealers computer this setting will change back to block you viewing TV in motion and if the software is ever updated this will be permanently blocked.
This only applies if you live in the EU or have an EU spec headunit, US headunits cannot play DVD movies.
Just for the record i don't think watching moves when your meant to be driving is a particularly clever idea, I'm not an expert but when i watch movies my eyes tend to focus on the screen but when i drive they focus on the road and short of taking one eye out and installing it into my hand i don't know how i could do both at the same time safely.
Not sure of his location so i won't make a blanket statement and say its illegal but in EU countries it is (and perhaps in the US also?) and your insurance will not be valid if they find out.
Also if this was a 4 door car and it was rear seat screens being talked about fine but its very hard not to get distracted by the images displayed on the screen when its playing back a movie (unless its a slow moving one)
In the UK, it's 100% "bad" , and if you are found with a "front mounted" video display (defined as a system playing video images in where the driver would be able to see them) you will be declared as "at fault" in an accident situation. I don't know that it's actually "illegal" - ie a copper would ticket you for it - but I've been told that's the case.
In any event, I find it a bit silly to drive and watch something other than the road - but I've got gray hair, so...