To take the photos, I set the camera up on a tripod, set both the focus and exposure manually and the tried to fire off photos at fairly regular intervals using a cable release. There was some trade of between depth of field and shutter speed, but I worked on the fact that the car would be that small in the frame and it didn't matter if it wasn't sharp all the way through the image.
In photoshop I then arranged opened the first two images as layers. I then erased areas of the top layer so that you could see the car coming through from the layer below. These two layers were then flattened and the third image introduced and the process repeated.
It was quite labour intensive but the result of the thirty images combined is shown below (click on the photo to open a larger example).
Whilst the result is far from perfect, it is a starting point and has given me a few ideas for some alternative uses of the technique.