Yeah carpc's are cool but they are way more expensive and require quite a bit of work to get to the functionality of that youtube video.
If you have days and days of free time, budget in the 1 to 2+ grand range and a ton of patience then a carpc can be yours.
It costs around $700 for a complete carPC system if you already have an amp setup. The biggest pain is the screen if you have a standard double din opening that won't fit a 7" touch screen (such as on many Toyotas and Scions).
Breakdown in pricing:
Lilliput Eby701 7" touchscreen $170
CarPC (includes power supply, dual core atom, 1 gig of ram, case, 200 gig HD) $300
Visteon HD Radio $60
StreetDeck $99 (RoadRunner is a free alternative but requires the purchase of additional navigation software)
GlobalSat GPS $34
Total: $663
It's certainly not cost prohibitive. In terms of setup, it's not all that difficult. Just install Windows XP and install StreetDeck. The plugins (digimods) are just addin downloads that you just download and double click to install. OneVoice only works with StreetDeck 1 currently though but an alternative is being developed that also supports voice controlled navigation (once the navigation is opened up in the SDK).
Doc