Bill Gates schemed to take shares in Microsoft Corp. from his co-founder during the early days of the software company following his partner's treatment for cancer, according to a new memoir by the billionaire co-founder, Paul Allen.

The allegation is part of a critical portrait in the book of Mr. Gates, with whom Mr. Allen formed a friendship in grade school that evolved into one of the iconic partnerships of American business. The book, "Idea Man: A Memoir by the Co-founder of Microsoft," is scheduled to go on sale on April 17. A draft of the memoir was viewed by The Wall Street Journal. An excerpt of the book appeared on Vanity Fair's website early Wednesday.

The book gives a revisionist take on some details of Microsoft's history and the relationship between Mr. Gates and his former partner, the two of whom have long been viewed as cordial if not close friends. The book has created a rift between Messrs. Gates and Allen, say people who know both men. In the book's acknowledgments section, Mr. Allen thanks Mr. Gates along with 17 other people for "general and logistical assistance."

The book is "a very balanced portrayal of their relationship," said David Postman, a spokesman for Mr. Allen. "Paul clearly values the input and the ideas and energy of Bill Gates."