using factory nav systems for dvd

ok, my understanding is that most of the factory nav systems use an RGB signal from the nav unit up to the monitor, so in order to integrate a DVD player you must find the video signal from the factory nav and splice into that with your new video signal with whatever your using, DVD, VCP, etc..  and you must convert the standard composite DVD video signal to an RGB signal, is this correct???? so if this is the case, as long as you can obtain the information on the factory video signal wire, and as long as you can convert the signal from your dvd to RGB this is possible?  and besides using the pioneer unit to convert the signal to RGB how else can this be done in a cost effective way?  i found a website that offers a kit for the lexus, $300 for the video integration, and $300 for the pioneer unit to convert the signal, but since i am an installer i want to be able to do this all by myself.... after all what fun is it if all you have to do is plug things into each other to make it work... anyone can do that...