Updated models with AMD graphics options expected in early 2017.
Apple Quietly Intros 64-Bit Windows Support in Boot Camp
Important: You must use a single full-install Windows installation disc (Service Pack 2 is required for Windows XP installations). Do not use an upgrade version of Windows and do not install an earlier version of Windows XP and attempt to update it later to SP2 or later. Use only 32-bit versions of Windows. If you have a Mac Pro introduced in late 2007 or later, you can use a 64-bit version of Windows Vista.
The finding has been confirmed by multiple users. No indication if these drivers will become available with the next Mac OS X update. Mac OS X 10.5.2 has been undergoing testing and is expected to be released in the coming weeks.
Leopard's Boot Camp feature allows owners of Intel-based Macs to natively boot into Windows.