There are two excellent books on Haitian voodoo that I can recommend. One is by Wade Davis entitled The Serpent and the Rainbow: A Harvard Scientist's Astonishing Journey into the Secret Societies of Haitian Voodoo, Zombies, and Magic. This book was published in 1985. Another good source is The Traveller’s Tree by Patrick Leigh Fermor. See chapter 11 in particular. The original was published in 1950 in England. The version I have is a reprint from 1986 that was published by Penguin Travel Library.
You can most likely find copies of these books on ABEbooks.com or Amazon.com. My copies are not for sale.
The most common spelling for this religion is voodoo. Other spellings include Vodun, Vodou, Vodoun, Vaudou, Vaudoux.