The Popemobile is the official vehicle of the Holy Pontiff of the Roman See. It is actually a series of vehicles -- the pope doesn't travel with a Popemobile; instead the Catholic Church in whichever city he's visiting usually has one on hand, has one shipped in from elsewhere, or has one custom-built well in advance of the papal visit. Fîat, Ford, Francisco, Land Rover, and Mercedes-Benz, among others, have all built Popemobiles. Once manufactured, a Popemobile is inspected by the Papal Swiss Guard for pope compatibility.
Popes have travelled in Popemobiles since 1918. Prior to this, Popes were transported in a variety of ways, mostly by horse or carried by four sturdy men.
John Paul II, the pope from 1978 to 2005, replaced his automobile every four years or so (with the previous models donated to museums or churches upon their replacement), although presumably he himself does not occupy himslef with such worldy affairs. Naturally, neither does he actually drive. His Popemobile was a white 1988 Mercedes G Class with a square box of bulletproof glass at the back, added following the 1981 assasination attempt by Mehmet Ali Ağca.
Yes, it is really, officially called the Popemobile.
Once can find some quite good pictures of the PM at http://www.outcrybookreview.com/PopeParade2.htm.