ok this seemed clear until I saw this
http://support.microsoft.com/?kbid=930985


On 23 Jan, 15:33, Bob I <bire...******.com> wrote:
> You are confusing Upgrading with aCleaninstallfrom anUpgrade
> version. Please read the following quote from:
>
> http://www.winsupersite.com/reviews/winvista_03.asp
>
> Understanding your installation choices
> How you acquire WindowsVistaplay a large part in any decision about
> how you will actuallyinstallthe operating system. At a high level, you
> have the following basic choices:
>
> Cleaninstall. With this method, you boot the PC from the WindowsVistainstallDVD, run interactive Setup, format the PC's hard drive, andinstallWindowsVistaas the only OS. This is probably the rarest way to
> getVistaon a PC. You can use a "Full" or "Upgrade" retail version of
> WindowsVistato perform acleaninstall, though you will need
> "qualifying media"--typically a Windows XP or 2000 CD that proves you
> qualify for theUpgradeversion.
>
> Upgrade. Here, you insert theinstallDVD from a "Full" or "Upgrade"
> retail version of WindowsVistawhile running Windows XP and perform
> what's called an in-placeupgrade. The Setup process is similar to that
> of acleaninstall, but most of your existing applications and all of
> your data files will be available and working properly once theupgrade
> is complete. Unfortunately, there are a number of qualifications to theupgradeprocess in WindowsVista. First, you can onlyupgradecertain
> versions of Windows XP to certain versions of WindowsVista. Here's a
> chart that explains which XP versions can be upgraded:
>
> DandyDon wrote:
> > Another thing to consider: TheVistaUpgradeonly installs from Windows, so
> > anytime you need a complete reinstall ofVista, you must first reinstall XP.
> > No more 'sticking the XP disc in for verification' beforeinstallas before.
> > So, keep your XP media. If OEM, get a copy of XP from your system
> > manufacturer if you don't have 'restore' disks with OEM XP on it.
>
> > Otherwise, you will be stuck. Your hard drive copy of XP will be gone, with
> > no way to restore it andVistawon'tinstallby itself.
>
> > IMO, your best option is to buy the retail version. It can be installed on
> > an empty disk.
> > "titus12" <titu...@msn.com> wrote in message
> >news:ugfH5wlPHHA.4376@TK2MSFTNGP02.phx.gbl...
>
> >>Will it be better toinstallVistaover WinXP Home or do acleanInstall?
> >>Will Zone Labs have an update ready whenVistagoes on sale?
>
> >>Thank you;
> >>David