The airplane, a four-engined heavy jet, was directed to taxi to an active runway. The taxi route would eventually cross an active runway. Ground control directed the airplane not to cross that runway. This command was acknowledged by the aircrew. The airplane stopped and held its southerly oriented position on the north-south oriented taxiway which intersected the active runway. While the airplane was stopped, a maintenance utility truck operated by another airline came to a stop on the east side of the service road which crossed perpendicular to the taxiway the airplane was positioned on. Ground control directed the airplane to continue taxiing. As the airplane began to power up, the service truck drove behind it. The truck was struck by the airplane's jetblast and rolled over two or three times. A review of the airport's motor vehicle operating regulations handbook and the airline's driver training program revealed the dangers of jetblast to motor vehicles were not covered.