Hi there
the tripod without flash is the first and probably the best thing to try (as mentioned in another post), also a higher sensitivity (ISO value) would allow the camera to take pictures at a higher shutter speed, but also gives rise to higher noise (graininess present as red and blue pixels mixed into the photo). Another way to minimise background blackout is to try and focus on another, further part of the car. By focussing on the licence plate/bumper, the camera will meter that and calculate for exposure values related to that distance and particular composition, thus having a well exposed bumper and a dark background. If it's possible to focus on, say the windscreen (taken from front for example), then the camera will calculate values to expose the scene correctly.
I hope this post hasn't been all "blah blah blah". Better luck with your next lot of photos!
Sal
