In terms of both quantity and quality there is a vast wealth of published first hand material that is only recently at odds with entries in modern encyclopedias such as Encarta 95. It would appear there is a recent move afoot to rewrite or suppress the history of the Incas.

In forming my opinion I read all the available English translations of the published reports of the Spanish Conquistadore, Franscisco Pizarro himself, and all the published reports and letters of the early Church in Peru.

I have read all the books about the Spanish Sergeant, Pedro de Cieza de León, and all of his published works.

Best of all, I have read both volumes of Garcilaso de la Vega El Inca's "Royal Commentaries Of The Incas." The second volume of this book was so embarassing to the Spanish, that is was not widely published until 400 years after it was written. It clearly shows the Incas were much more advanced than the Spanish in many areas of endeavour including both Metallurgy and Astronomy.

I have also read all 27 works of the British scholar, William H. Prescott, analysing Inca culture from many perspectives.  I find his work accurate and far more informative than anything and everything that Bill Gates and his friends have to say about the Incas and their culture.