mounting a DVD screen to a roof lining....

ideas ??

On an angle or flat? easiest is to use very strong contact adhesive to glue either some MDF to screw a mounting box into, or glue the box directly (having cut an x into the head liner for the box to fit through, just fold the fabric back or cut the rest of the square out bearing in mind the hole must be slightly smaller than the box outer flanges to make a tidy edge.)

the head lining is that fury plastic type, the bit I want to mount to is not flat but the bit that holds the screen has a mounting plate that is.. its a fold away screen

What?
I think i know what you want!

Its one of those screens that folds flat into the base unit, what you need to do id make a plate you can use to flatten a section of the roof out to mount the screen properly, this may need some serious glue/screwing into supporting members for the roof.

is "no nials" type stuff up to holding a 6" square piece of MDF onto the roof for this or.. do I need to secure it with screws from the roof side before i attach anything to the inside ?

In the interest of safety you really need to escure the board properly to the sides of the roof, as the forces involved in an accident (hoping you never have one) could easily dislodge no-nails glue.