If Vista archives the old Windows installation, does that mean that in some
future version of Vista the user will be able to uninstall Vista and restore
his old version of Windows?
NT upgrades to an NT-based system have never offered a revert option. That
only occured when doing an NT upgrade to a 9x system (like Win98-->WinXP),
and only under certain conditions (no file system conversions or upgrades to
the service pack level among them). I suspect that this "undo" will likely
not be a feature of the release product, though there's still nothing set in
stone yet.