Learn how to uninstall and remove Windows Vista Service Pack One from your Vista computer using the Command Line:
Click Start, expand All Programs, and expand Accessories.
Right-click Command Prompt, and then click Run as administrator.
In the command window, type the following and press ENTER:
start /w pkgmgr /up: VistaSP1-KB936330~31bf3856ad364e35~x86~~6.0.0.<build number>
To uninstall SP1 from a 64-bit computer, replace x86 with amd64 in this command. Replace <build number> with the appropriate build number you are uninstalling. For example, for the Vista SP1 RC Preview, the build number is 17042.
Wait for the command to complete (there is no progress indicator), and then restart the computer when prompted.
To confirm that uninstallation of Vista SP1 was successful, click Start and type winver in the Start Search box. The reported build version should be 6000.