If you are running Win2k or XP x86 you cannot upgrade to Vista x64. You can
only upgrade to Vista x86. Period. You can only install Vista x64 from a
full edition.

The only legacy Windows you can run a Vista x64 Upgrade Edition on is XP Pro
x64.

An upgrade dvd will boot the system. However when you type in the upgrade
product key you will be prompted to reboot and run Setup from your legacy
system desktop. The x64 Setup.exe will not run on an x86 desktop.
Therefore it is not possible to use an x64 Upgrade Edition on a computer
running an x86 legacy version of Windows.

"Grungeon" <Grungeon@discussions.microsoft.com> wrote in message
news:03D286C1-5BA2-4B8B-9D27-4A67AD3F03C4@microsoft.com...
> Hello, I've been reading many of the posts about upgrading 32bit XP to
> 64bit
> Vista.
>
> People seem to agree that the retail upgrade disk will be bootable for
> troubleshooting purposes.
>
> However, there still seems to be controversy as to whether a person can
> install 64bit Vista as a bootable disc. So far, the discussion tends to
> favour that it won't be possible.
>
> Can anyone provide a once for all answer, from experience with an actual
> Retail Upgrade Disc or definite knowledge from Microsoft? This would also
> help others with this same question, without need to read through all the
> posts.
>
> Thanks.