from :
*support.microsoft.com/kb/948537
To uninstall Windows Vista SP1 by using the Programs and Features item in Control Panel, follow these steps:
1.Click Start*support.microsoft.com/library/images/support/kbgraphics/Public/EN-US/VistaStartButton.jpg, type Appwiz.cpl in the Start Search box, and then click Appwiz.cpl in the Programs list.
*support.microsoft.com/library/images/support/kbgraphics/Public/EN-US/SecurityShield.jpg If you are prompted for an administrator password or for a confirmation, type the password, or click Continue.
2.Click View installed updates.
3.Click Service Pack for Microsoft Windows (KB936330), and then click Uninstall.
4.Follow the instructions that appear on the screen to complete the uninstall process.
Method 2 :
Important Before you use System Restore, make sure that you have restarted the computer at least one time since you have installed Windows Vista SP1. By restarting the computer, you allow for any remaining servicing processes to finish.
1.Click Start*support.microsoft.com/library/images/support/kbgraphics/Public/EN-US/VistaStartButton.jpg, type rstrui in the Start Search box, and then click rstrui in the Programs list.
*support.microsoft.com/library/images/support/kbgraphics/Public/EN-US/SecurityShield.jpg If you are prompted for an administrator password or for a confirmation, type the password, or click Continue.
2.In the Restore System Files and Settings window, click Next.
3.In the Choose a Restore Point window, click Install: Windows Vista Service Pack 1, and then click Next. Or, click a restore point that was created before you installed Windows Vista SP1, and then click Next.
Note The "Install: Windows Vista Service Pack 1" restore point is the restore point that was created immediately before you installed Windows Vista SP1.4.Verify the restore point that you want to use, and then click Finish.