Rotating object

Does anybody have a suggestion for how to compute the rotation calls necessary to rotate an object to be aligned with a given normal. For instance, say I have a model of a car that is to be drawn over a heightfield composed of triangles. What can I do to keep the car tilted to the same angle as the ground it is sitting on?

Similar question was handled here:

Cars are fairly easy to make follow the ground if you keep track of each wheel. Just tie each wheel to the car frame by way of a strut, and the car will almost naturally follow the terrain. If you use struts, be sure to use some springs on them to dampen the transients.