Here's what you should know before you install SP1. Microsoft recommends users fetch the service pack using Windows Update (a 65 megabyte file for most users), but anyone who needs to install the update on multiple computers can download a standalone installer click here (>450 mb).
Microsoft says that for Windows Update and stand-alone installations, the SP1 setup program automatically creates a system restore point before the installation of SP1 begins (system restore backs up critical system files). But Redmond suggests that Vista users "may want to back up any user data before you begin installing SP1." Vista includes a backup utility called the Backup and Restore Center that allows you to back up certain files or make a complete backup image of the hard drive where Vista is installed