The 36-page booklet, titled Willy the Wizard, was written in 1987. According to the statement from the estate, "both Willy and Harry are required to work out the exact nature of the main task of the contest which they both achieve in a bathroom assisted by clues from helpers, in order to discover how to rescue human hostages imprisoned by a community of half-human, half-animal fantasy creatures."
According to Bloomsbury Publishing Plc (who publishes the Harry Potter series in the UK), these claims were first made in 2004 by attorneys working for Jacobs' son, but the accusers were not able to present any text from the Potter books that plagiarized Willy the Wizard. In their own statement on the matter, Bloomsbury says that Rowling "had never heard of Adrian Jacobs nor seen, read or heard of his book Willy the Wizard until this claim was first made in 2004." Harry Potter and the Goblet of Fire was published in 2000. [Reuters via Yahoo! News]