If possible, place it on the roof of your vehicle.

If the antenna was placed inside the car, the signal stength would be weakend because it would have to go through the cars body. Also, if you start using higher powered antennas and wireless cards, you could be putting yourself at risk for health problems because the signal is bouncing throughout the car.

The easiest approach is to purchase a 12VDC/120VAC inverter. These units will plug into your cigarette lighter plug in a car and produce 120 volts AC (the same thing that is in your house). You can plug your laptop charger into it and it will stay up as long as you need.

In some states, such as California, it is illegal to have a laptop in the front seat while the vehicle is moving. This law was obviously created in order to prevent people from getting into accidents because they were looking at a computer.

Realistically, nobody is going to pull you over unless you are actually looking at it. A good idea is to go wardriving with a friend so he can hold the laptop and monitor it. If you must go wardriving solo, then put the laptop under the seat or close the lid.