Dan Warne has the story in Australian Personal Computer:
Microsoft revealed today that it will not support EFI booting for Windows Vista on its launch. The news will be a shock for owners of Intel Macs who had hoped they would be able to dual-boot between Windows Vista and OS X. Intel Macs only support booting via EFI.
Speaking at Intel Developer Forum San Francisco, Microsoft development manager, Andrew Ritz, also revealed that there will never be any support for booting Windows via EFI on systems with 32-bit processors.
Although Microsoft has previously said EFI booting would be supported by Vista, Ritz admitted that EFI support won’t be seen in any version of Windows until the release of Longhorn Server.
Extensible Firmware Interface (EFI) is the Intel-developed successor to Basic Input Output System (BIOS) as the built in code that gets a PC up and running before handing it over to the operating system. One interesting aspect of EFI is that it allows the development of operating system independent device drivers which would be stored in flash memory instead of being artifacts of the operating system.
Since Microsoft has been promising for some time that Vista would support both BIOS and EFI, this revelation was a shock and theories abound as to what happened. Beyond the obvious possibility of a need to drop features to get Vista out on time, there are suggestions of a Microsoft preference to not put a lot of effort into anything that encourages “operating system independence.”