Windows Server 2008 and Windows Server 2008 both use NTFS version 5.1. Does this mean that a disk that's used in one platform could be moved to the other and "just work"?
The answer is "Yes, except…"
Specifically, if a disk is formatted on Windows Server 2003, you can mount it on Windows Server 2008 and use it without any issues. And if a disk is formatted on Windows Server 2008, you can mount it on Windows Server 2003 and use it without any issues.
But if you have a disk mounted on a Windows Server 2008 system and the system crashes, leaving the disk in a dirty state, and you then mount that disk on a Windows Server 2003 system, transactional consistency will be lost since Windows Server 2008 NTFS supports TxF while Windows Server 2008 NTFS doesn't. And if you had volume snapshots on the disk, they may lose their consistency and be unavailable once you mount the disk on the downlevel system.