Here's a picture of me using my simple flamethrower at BurningMan'98 (click it for a much larger image). It creates a flame of variable lenght and width, the best range I got was about 20 feet.
The week before Burningman '98 I constructed my first flamethrower.
My flamethrower experience nearly ended in disaster at BurningMan when a pressurized tube broke free and sprayed kerosene up my entire body. A hose clamp had not been attached at a critical location.
The device I built is so unsafe that I do not want anyone basing their own on my flawed design. I include a description here only for educational purposes.
The flamethrower is basically two parts: a pressurized fuel filled chamber and a hand valve attached to a nozzle.
The Fuel chamber is a metal insecticide sprayer with rubber valves available from just about any hardware supply stores. Since the valves are rubber it is VERY important to only use kerosene with this device - Gasolene and Alcohol Spirits will dissolve the valves.
The Standard sprayer is replaced with fuel line and a gardening sprayer hand valve, with a few additional feet after the valve to a standard gardening variable nozzle.
To fire the gun you merely pressurize the chamber with the built in hand pump then pull the trigger, while aiming at an already burning object. The fluid comes out the nozzle and creates a wonderful fire.