The 70-642 was introduced in 2008. Like other tests, it can be refreshed from time to time to maintain relevancy. It would be beneficial if you have a look at the latest skills measured, as published on the 70-642 web page:
http://www.microsoft.com/learning/en/us/exam.aspx?ID=70-642&locale=en-us#tab2
By looking at the skills measured, you can determine if the study material you are using is covering all of the topics. When you run across items in the skills measured section that are not covered by your study material, you can make study adjustments
(use TechNet, labs, etc. to acquire more skills in those sections). Sometimes, you can match up chapters in a book with the skills measured and quickly see what isn't covered in the book. Often, books are written early in the lifecycle of the product.
The second edition of the book would probably be quite valuable in your preparation.
Also, have a look at your exam printout - it can sometimes be helpful in pinpointing areas that need additional study.
Brian
