People at StreetDeck took the Windows XP based Viliv S5 and installed their user interface on it. S5 has built-in GPS, Wi-Fi, USB port, mini USB, monitor port, resistive touch screen.
It comes with a suction cup window mount which you can see in the video below, and of course a car charger as well. The video demos the GPS navigation, XM radio, and other general features of their StreetDeck II user interface.
Streetdeck swears this is the best UMPC as far as delivering GPS navigation features be it the really fast resume time, or the sensitive touch screen. Speakers are also very good which can let you listen to music while getting driving directions. It is an XP based PC after all.
Viliv S5 w/ GPS, car kit, and StreetDeck II costs about $700. It will be ready soon after March.