The Windows Vista Product Guide provides a comprehensive overview of the innovative features and functions that make Microsoft® Windows Vista™ the next-generation Windows client operating system and successor to Windows XP. This guide also provides information the benefits Windows Vista offers diverse users as well as information about the different editions (SKUs) available. It's about 300 pages, and contains a lot of really great information about Windows Vista. Definitely a must-read!
You can find direct download links to the Windows Vista Product Guide and the XPS Viewer on Fred Pullen's blog.