well ijust set up a small tripod in the back seat of my friends car. and it worked just fine. try a small one like the cheap 29.00 ones. put two legs on the floor of the car and one on the seat. make the legs different lengths of course so its level.
it is amazing how much better it looks than hand held.
i doubt it would work good with the dvx100. you can already see quite a bit of oscillations due the weight of the cam in the videos.
with a small cam, one i placed it on the tripod, on the car frontal part, pointing at the driver. lots of duct tape and it worked great. obviously i wouldnt risk the same procedure with a dvx100