Microsoft Press has just released the Microsoft Windows Group Policy Guide, an 800-page reference guide for learning about and managing Group Policy within the enterprise.  This book was co-written by industry-expert Darren Mar-Elia, Derek Melber, William Stanek, and the Group Policy Development team. 

The description of the book:

Get the in-depth information you need to use Group Policy to administer your enterprise system—direct from industry experts and the Microsoft Group Policy team. With Group Policy and Active Directory® directory service, administrators can take advantage of policy-based management to streamline the administration of users and computers throughout the enterprise—from servers running Windows Server 2003 or Windows 2000 Server to workstations running Windows XP Professional or Windows 2000 Professional. This essential resource explains how to simplify and automate administrative tasks, including policy enforcement, system updates, and software installations, as well as how to centralize the management of network resources. The CD provides essential utilities, custom ADMs, GPO spreadsheets, and more. It’s everything you need to help increase your efficiency while bolstering user productivity, security services, and system reliability.