actually they already made flying cars.. prototype at least.. i still remember one that took up 2 full pages of the new paper several years back. and YES it flew, landed, and drove as per normal.
the most famous flying car is "SkyCar" by Moller which is capable of vertical takeoff and landing - the standard method of flight for all flying car prototypes.
check out
http://www.moller.comif i'm not wrong the M400 was the one the new paper featured several years back, of course the one on the website is the latest M400..
also in 1973, Ford (car maker) and Cessna (plane maker) made a hybrid one.. it crashed, killing the developer.
however, the one i'm REALLY interested in is the Terrafugia Transition
http://www.terrafugia.com/vehicle.htmlxD