"Windows could not update the computer's boot configuration..."

I am attempting to upgrade from Win XP Pro (SP3) to Vista Home Premium, and
purchased the update from the Microsoft Store online and downloaded my three
files. That is, I am not using the CD or DVD option for upgrade.

The Windows Upgrade Advisor gives me the all-clear for upgrade.

When I commence the upgrade process and get to the 'Installing Windows...'
screen it successfully completes the "Copying Windows Files" task but then
fails at 27% through the "Expanding Files" process.

I receive the error message "Windows could not update the computer's boot
configuration. Installation cannot proceed."

This problem is described in support article KB931697. I have taken the
remedial actions (registry edit) described in that article, but the problem
is not resolved. When I go back into the registry now, the setting is as it
should be according to the knowledgebase article, so it is not the case that
the fix is being reversed by other software.

Has anyone else come across this? Any ideas as to how I can get my upgrade
to work successfully?

Thanks in advance for your comments.