There are many display options when putting a computer into a BMW. Some of your choices are determined by which model you have and what options it has installed.
Firstly let me make one thing clear, to get the best out of your Carputer do not use a non-VGA screen.
OK with that said let's go through the main choices available.
Fabricate the screen into a double DIN size whole in the dash.
Flip out monitor in a single din slot in the dash.
Monitor on a swivel stand stuck on or protuding from the dash.
Fabricated into the sun visor.
Each of these will be discussed in more detail below.
Fabricate into Double DIN
In my opinion this is the best option. Why? Well it is the one that probably looks the most OEM. ie it looks like it was intended by the manufacturer. and is the most aesthetically pleasing
Flip out Monitor
This is probably one of the easiest options available, however it can be fraught with problems. Going this way you have two choices.
Non - Motorised
From reports so far, the motorised have been more problematic than the non - motorised ones, however they do have that extra WOW! effect.
This certainly the easiest to do, however it probably is the least likely to look like it doesn't belong there, and thus being it is more likely to attract unwanted attention from scumbags unless it can easily be removed whilst parked.
This can look quite neat but I would say not the most pratical to use. Good as an extra monitor but I wouldn't recommend it as a primary monitor.