A new detailed whitepaper on BCD, EFI, WMI is available.
“Microsoft has completely reengineered the boot environment for Microsoft Windows Vista to address the increasing complexity and diversity of modern hardware and firmware. One aspect of this reengineering is a new firmware-independent data store that contains configuration data that influences the boot process. This paper provides an overview of this configuration data – called boot configuration data (BCD) – and describes how to use the related tools to manage boot options.”
The following is here : http://www.microsoft.com/whdc/system/platform/firmware/bcd.mspx