Install a 64 bit OS on a 32 bit system

How to install Vista 64 bit or Windows 7 64 bit on your computer that has Windows XP 32 bit as dual boot. Retain the same drive letter under XP, Vista, and Windows 7. Or choose a drive letter other then C: for Vista and Windows 7.

This work around is not for the faint of heart, but does work. The bellow example is with two partitions. It can be done with more partitions it is just more difficult.  It can also be done with any combination of Operating Systems.

Make a full verfiable backup of your computer hard drives before starting. Backing up is a rule not an option or only an option if you are a fool.

Here is how:
Under XP change the drive letter of your DVD-ROM, Other Drives to something other than the drive letter you want to have your Vista or 7 installed. Make sure the target drive letter for your installation of Vista or Windows 7 is free. For this example we are going to use V: as the target for the install but you can use any free drive letter.

Boot from Vista or Windows DVD, click "Install Now" and hit Shift+F10, start diskpart and make any partition changes you need. A safer way is to use a partion manager in Windows XP and make any partition changes and make a partition V:

Install Vista or Windows 7 as you would normally installing on the empty partition you just made (make sure that "Automatically activate when connected to internet" is unchecked so you don't have to activate Vista twice -- you'll see the reason for that later). Also don't install any updates or non-disk-essential drivers. What you are going to do is a intial install of Vista or Windows 7 and then reboot and install fully.

Once you log in to Vista or Windows 7 for the first time your operating systems drive letter will be C-- open to registry editor and go to HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices. Then rename \DosDevices\D: to something else for now (presumable this is your XP partition), rename \DosDevices\C: to \DosDevices\[DESIRED_VISTA_OR_WINDOWS_7_DRIVE_LETTER]:(where [DESIRED_VISTA_OR_WINDOWS_7_DRIVE_LETTER] should be replaced with the desired drive letter for Vista or Windows 7 partition). In our case V: Now rename previously renamed \DosDevices\D: to \DosDevices\C: if your Win XP was C: (see How to restore the system/boot drive letter in Windows)

Close regedit and reboot. Now if you boot into Vista or Windows 7 you will not be able to run anything and your profile will not be loaded -- so instead of booting normally choose Safe Mode with Command Prompt (by pressing F8 on boot menu screen while Vista or Windows 7 option is highlighted). Once you boot into Vista or Windows 7 Safe Mode with Command Prompt change drive to your DVD drive and start Vista setup AGAIN by typing setup in command prompt.


Some people that have done this have gotten a normal functioning Safe Mode. I did not. All I was faced with was a screen with Safe Mode in the four corners. Fear Not. Hit Ctrl_Alt_Delete to bring up Task Manager. Choose File > New Task (Run....). In the Create New Task box type CMD  and press OK which brings up the Command Prompt. Change the drive letter to your DVD/CD drive with the Vista or Windows 7 install CD in the drive. Use CD YOUR_DVD_DRIVE_LETTER: example: CD H:
You may have to try a few drive letters to find what your DVD drive letter. After you are at your DVD Drive type: setup

or Windows 7 Go through Vista installation again and enjoy same drive letter assignments under XP and Vista. Your Vista or Windows 7 install will be on a new drive letter like V: in this example.