Windows Server 2003 (both 32-bit and 64-bit) and Windows 2003 x64 Editions support only GPT partitions as a data volume. Itanium computers support GPT for both boot and data volumes. Windows Vista and Windows Server 2008 (both 32-bit and 64-bit) support GPT disks with Extensible Firmware Interface (EFI)-based systems capable of booting from an EFI volume. Windows 2000 and prior Windows' versions won’t recognize GPT disks.
Microsoft has a GPT FAQ at Windows and GPT FAQ.