[Update: This is for adding Vista to Windows 7 Boot Manager. For adding Windows XP, please see this post.]

Ok, you have installed Windows 7 Beta on your Vista machine, and you cannot boot to Vista any more. What can you do? This is exactly what I ran into. Let me tell you how to fix it.

My testing machine was set up to dual boot Windows XP and Vista. XP was on C: drive and Vista was on D: drive. When I installed Windows 7 Beta, I installed it on C:. After the installation, I could only boot to Windows 7. The boot option for booting to Vista on my D: drive was gone. The boot manager for Windows 7 is the same as Vista. Therefore, I was able to figure out a way to add Vista to the boot manager. Here are the steps:

1. Invoke a command prompt with Administrator priviledge. If you don’t know how to do it, please follow the steps in this post. The instructions are for Vista, but they are the same.

2. Type the following to list the current boot manager settings.

C:>bcdedit

Windows Boot Manager
--------------------
identifier              {bootmgr}
device                  partition=C:
description             Windows Boot Manager
locale                  en-US
inherit                 {globalsettings}
default                 {current}
resumeobject            {59cad9f2-de83-11dd-9d9e-c59ac6c2613b}
displayorder            {current}
toolsdisplayorder       {memdiag}
timeout                 30

Windows Boot Loader
-------------------
identifier              {current}
device                  partition=C:
path                    \Windows\system32\winload.exe
description             Windows 7
locale                  en-US
inherit                 {bootloadersettings}
recoverysequence        {59cad9f4-de83-11dd-9d9e-c59ac6c2613b}
recoveryenabled         Yes
osdevice                partition=C:
systemroot              Windows
resumeobject            {59cad9f2-de83-11dd-9d9e-c59ac6c2613b}
nx                      OptIn

3. Type the following to create a Boot Loader based upon the default boot loader.

C:>bcdedit /copy {current} /d "Vista"
The entry was successfully copied to {59cad9f6-de83-11dd-9d9e-c59ac6c2613b}.

4. Type the following to change the device to D: drive. Note that the identifier is the one generated by step 3. This id is different for every boot loader. You have to replace it with the actual output when you create the boot loader.

C:>bcdedit /set {59cad9f6-de83-11dd-9d9e-c59ac6c2613b} device partition=D:
The operation completed successfully.

5. Type the following to change the osdevice to D: drive

C:>bcdedit /set {59cad9f6-de83-11dd-9d9e-c59ac6c2613b} osdevice partition=D:
The operation completed successfully.

When you are done, reboot the machine and you’ll see the option to boot to Vista.