Recently I set about a reinstall of Windows XP which is on the system drive, drive C. Windows Vista is installed on drive D and all the boot system files for both XP and Vista are on the XP installation drive. One can make sure which is the System drive by going to My Computer>Right click>Manage>Disk Management and look for the drive/partition tagged "System".

The problem here is that when formatting the XP drive, if XP is installed on the System drive, one will lose the ability to boot to Windows Vista. If the steps below are taken, then one can easily restore the ability to boot to either Vista or XP after the reformat and clean install of Windows XP is complete.



Preparation

I did not want to disturb my Windows Vista installation, so this is the process I followed:

Copy and paste the folder Boot to the drive on which Vista is installed
Copy and paste the file bootmgr to the drive on which Vista is installed
As a precaution, create a backup of the BCD Store with VistaBootPRO and select the drive on which Vista is installed as the save location.
Uninstall the Vista bootloader using VistaBootPRO, from the Bootloader page.
Delete ALL entries from the Manage OS Entries page of VistaBootPRO

Once this was done, I rebooted to the Windows XP CD and reformatted and reinstalled Windows XP.


Reinstating the Windows Vista Dual Boot

After I had installed all drivers and some of the programs I use to Windows XP it was time to get my dual boot with Vista working again. Here is the process to follow to resinstate the dual boot:

Downloaded and install VistaBootPRO.
Cut and paste the folder Boot from the Vista installation drive back to the XP installation drive
Cut and paste the file bootmgr from the Vista installation drive back to the XP installation drive
Go to the Bootloader page of VistaBootPRO, select "Reinstall the Vista bootloader" and Apply

Reboot and you will find that the dual boot menu to both Windows XP and Windows Vista has been restored.