Well sometimes you can manually install the windows XP drivers and for each one set the file properties under compatability mode to XP SP2. While I was still testing the beta version, the nvidia 7800 graphics card had no vista drivers and then (last August or so) nvidia proudly proclaimed they wont release or even bother with vista drivers until november (business launch) so I was pretty much screwed there. So I took the XP drivers, and vista kept yelling at me saying what I was doing could corrupt the OS, and to stop what I was doing immediately. It even deleted the file once because it thought it was malicious activity I guess. I think they backed off the guarddog security a tad from then, but anyways, I set the drivers to run in compatability mode XP SP2. They worked ok, but not great. Sometimes random freezes, random resets, sometimes it would just not boot, until a reset cycle again.
So to sum up, try compatability but if you can get it to even work, it will be shoddy at best.
And why are you running Vista in the car anyways?! Dont get me as a "I hate Vista" bandwagon person. Microsoft sent me a copy free end of last summer to test (I think I was in the middle group of people they let in to beta legally), but honestly, right now no vista features will be helpful. In a year maybe then sure. But forntends are no good in vista, the Aero interface will always be hidden, it runs slower, and unless you do a lot of wifi connecting or cell dialup, the "new" security features wont do anything, so why vista in the car?