License plates

My understanding is that in many states, the Department of Motor Vehicles Records indexed on license plate number, and containing the name, address, and other information about the owner, is public or semi-public. How would an interested party go about finding this information? How difficult or costly is it? And what all is actually listed in the record? How about medical records? How private are they? How about other records which are, to me, private or appear to be private, but can actually be read by anyone without my consent? Kragen