When you insert a Windows Vista 64-bit DVD within a 32-bit operating system, and setup is launched, the operation is unsuccessful, and you receive the following error message:
Setup cannot run on this version of the Operating System. To install Windows please try booting from the install media.
When you try to upgrade a computer’s operating system from the 64-bit version of Windows XP Professional (x64) to a 64-bit version of Windows Vista, the upgrade is disabled. Note
If you have a 64-bit version of Windows Vista installed, you can upgrade to an allowed 64-bit version of Windows Vista. For example, you can upgrade Vista Home Premium to Vista Ultimate.
This behavior occurs because Windows operating system upgrades are supported only between matching operating system architectures. A 32-bit version of Windows XP does not recognize the 64-bit Windows Vista installer engine.
If you have a 32-bit version of Windows XP and want to install a 64-bit version of Windows Vista, you must boot the computer from the 64-bit Windows Vista DVD and then perform a custom installation of Windows Vista. Back up data before you start the custom installation.
This behavior is by design.