NT4 has native NTFS4 support, W2000 (5.0) has NTFS5 support and Windows XP
(5.1) has NTFS 5.1 support.
NTFS is also past-and-future-proof to some extent, meaning you can still
access NTFS5 from both NT4 and XP. NT4 support for NTFS5 is limited, not all
attributes are known, etc, etc, but you can still read files to back up.
