Fact is, ranchers use what can be considered flamethrowers in order to burn brush piles and things like that. To them it is a tool. Some of the best places to find information on making them for yourself, making your own fuel or how to use them without setting yourself on fire can be found on ranching and farming message boards.
You can also download the .pdf for a book called "breath of the dragon" that some fruitcake militant wrote.
From what I have read, the hardest part is making your own fuel that works reliably at different temperatures.