Roberto, the issues with using one of those screens as any kind of display, other than what it is designed for, would be very tricky. If you want to just use the display, you would need to design a driver circuit and the proper firmware/software to drive the display. So this would require first to obtain all the possible data for the display,.i.e. frequencies etc. Than you have to design the circuit board to drive those, or you would have to at least find the driver circuit.
If you wanted to use the iPad as anything else but what it was designed for, you would have to rewrite the firmware/ software driver for this. You will have to disassemble the code for the firmware, rewrite it with the proper codes. You can take a look at the pinout for the dock connector right here and see if you can design an A/V input for it. Not saying that it can't be done, but it will definitely require some heavy duty reverse engineering and circuit bending. Good Luck and let us know how it is going.