Apple said it won't preclude its users from installing Windows XP on their new Intel Core Duo based computers but according to BetaNews it won't be possible because of restrictions in Windows XP.
The new Apple computers use extensible firmware interface (EFI) rather than BIOS, and this would make it impossible to run Windows XP on these systems.
With the switch to Intel processors, Apple also moved from Open Firmware to EFI, which is an updated BIOS specification developed by Intel. Advanced features include the ability to boot into an EFI shell and run diagnostics and power up the CPU into a fully functional state immediately.
EFI also separates the control of devices from the operating system, meaning it can initialize hardware before loading the OS. This feature would allow for a system to connect to the Internet and download updated drivers before booting up.
The 64-bit version of Microsoft Windows XP does offer support for EFI but unfortunately that version only runs on 64-bit processors and the Intel Core Duo doesn't have the 64-bit extension.