It can be a pain ligning up the reciever with the satellite so it certainly wouldn't work as you drove round but when parked up it can get a lock.
The Sat reciever will not be very aerodynamic so perhaps get one that you take out and put on the roof when you want to use it.
Caravanners have sat dishes so it is possible - just a bit of a pain. (
Cable TV will not work very well in a car though
- only joking!)