How to Remove Windows Vista SP1 from your computer ?
You can remove SP1 by using either Programs and Features or the command line. Note, however, that you cannot uninstall SP1 offline using any method. In addition, it is not possible to uninstall the permanent prerequisite updates (KB937287, KB935509, and KB938371). However, you can uninstall KB936330 and KB937954. You also cannot uninstall the service pack and other updates that were installed using an integrated installation.
To uninstall SP1 by using Programs and Features
1. Open Control Panel, click Programs, and then click View Installed Updates.
2. In the Microsoft Windows list, right-click Service Pack for Microsoft Windows (KB936330), and then click Uninstall.
3. When prompted, restart the computer.
To uninstall SP1 by using the command line
1. Open an elevated Command Prompt window (click Start, type command in the StartSearch box, right-click CommandPrompt, and then click Run as administrator).
2. Run the following command (assuming that Windows6.0-KB936330.exe is in the C:\temp folder): C:\temp\Windows6.0-KB936330-X86.exe /x:C:\temp
3. To create a sandbox, type md <sandbox>.
4. To remove SP1, type start /w pkgmgr.exe /m:c:\temp\Windows6.0-KB936330-X86.cab /up /s:<sandbox>.
5. After Pkgmgr.exe completes, you will be prompted to restart the computer (unless you specified the /quiet command with Pkgmgr).