Just to make it clear, if i buy OEM NAVI, it'll plug in straight up?
 

I work @ the dealership and we deal with a bodyshop... my radio on my 03 just went and they have a wrecked G35 2004 Coupe with OEM navi in it, the car might be written off, and i wanna make a deal with a bodyshop owner to sell it to me..... I have some questions, will it connect straight up, meaning do they all come prewired for NAVI or after buying it, ill need to hack my harness?
2) Where does the DVD unit mount in the car?
Has anyone every done the complete plug and play?

no it doesn't bolt right up, try a search...

It's not worth the time effort and especially $$$$.

all you will need is the harness, screen with controls and the nav unit. do a search, there are 2 people here that i have done it.

Add to this list a lot of knowledge of electronics/schematics and a lot of patience.

A DD conversion is better and simpler.

You won't need electronics knowledge if you swap the harness out, that is pretty straight forward, just time consuming.

If you want to make your own harness, like the 2nd guy did, then you will need to read the schematics and make sure you are connecting things right.

It can be done, but it isn't plug and play.