Ive already got Nav.. and I aint using Linux in the car..
Got a good Nav package, which does Europe too, with all the postcodes, voice nav and visual etc.. (it works in Windows or Linux) - Got a deal on it when I bought the GPS Mouse.
Yea, was going to get a normal screen, but then found this 7" VGA Touchscreen, so no mouse/keyboard or anything, and crystal clear (You can read 10pt text on it at 1600x1200 apparently).
Both the screen and power supply are from America - cant seem to get them here!