Still, a fully integrated DVD/MP3/GPS system is something I'd want if it worked well...

The hardware is out there now to do this, touchscreens are cheap, and multiple software applications for touchscreen for this kind of stuff. The best I've seen so far is Coyote MediaCar, it actually embeds mappoint 2004 and looks very polished. This Is the main site but it's not up yet, This is the horrid website where you can actually download the app (beware it's french). There is also media engine (which is touted to be the best) but I didn't care too much for it, and about 10 or 20 more contributions, some even utilizing voice control, all freeware. I would guess that system is probably running XP embedded (just a guess).