My friend just gave me a book Preschool for Parents: What Every Parent Needs to Know About Preschool. It is by Diane Trister Dodge and Toni S. Bickart. It is new, published 1998 by Teaching Strategies and Sourcebooks, Inc. I'm not sure if it can be found in bookstores.
ontact info -
Teaching Strategies = 1-800-637-3652
info AT TeachingStrategies.com
It describes the elements of a good preschool, provides checklists of what to look for, concrete examples of what you should NOT see, suggestions for further reading, and references to WWW sites.