I tell you what - all the hassle associated with doing any of the mods suggested above wouldn't be worth the effort - just get factory nav and a video module, it's dead easy.
However, if you search back a fair way, there are some posts by woodman438 describing how to get signals into the screen and what kind of screen it is etc. Some useful info there, but he ended up just buying a video module anyway as it was too hard!
Then there are the problems you'd have with relocating the speedo (or tacho if you're in aus) as there are core modules behind it that aren't easy to deal with the relocation of. Not impossible mind, but certainly not easy!!