I'm just curious about the fact that you put a xp 1800 in your car ? Why so much power ? do you wanna rip dvd's in your car *g*
don't take this personal just thinking this is a bit much for car entertainement system-
For the xenarc there was a thread in LCD section with people who weren't wvery happy with it -
If you have the money buy a vga LCD with controller - If you wanna cheap screen buy a 5.6" or bigger RCA screen.
where to put the screen:
RCA screen : you could try fixing the mountig thing(sorry im not english) inside the ventilation
or build part that would fit between the ventilation and speed control console ( sorry cannot express me better ) so i decidet to make a pic
For GPS I just bought a little USB GPS receiver which should be great ( will receive it monday )
like you didn't mention OS - I did very good experiences with WInXP professional- no bluescreens and very fast boot !