If you have upgraded no options to revert back , however if you did a clean
install we do have an option as previous version of Windows files are saved
and are intact in Windows.old folder on primary root partition.
If that is the case then try these steps ..
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1. Check if you have enough disk space to install the new desired OS.
2. Boot into WinRE using the Windows Vista Media and open a Command Prompt.
To do this:
a. Insert the Windows Vista media in the computer’s DVD/CDROM drive, and
then restart the computer.
Note: To start the computer from the Windows Vista Beta media, the computer
must be configured to start from the DVD/CDROM drive. For more information
about how to configure the computer to start from the DVD drive, see the
documentation that is included with the computer, or contact the computer
manufacturer.
b. When the "Press any key to boot from CD" message is displayed on the
screen, press a key.
c. Select the System Recovery Options.
d. Select the Command Prompt.
3. Rename the following folders:
a. Windows
b. Program Files
ren Windows Windows.vista
ren “Program Files†“Program Files.Vistaâ€
rd “Document and Settingsâ€
- Copy the content of the WINDOWS.OLD folder to the root:
Xcopy /s c:\WINDOWS.OLD\*.* c:\
E:\boot\bootsect /nt52 c: (E: assuming as DVD/CD drive.
7. Close the Command Prompt window and click on Restart.
All the best If you did a clean install.