Windows Vista Service Pack 1 RC1

Vista SP1 release candidate 1 is available now via Windows Update. The first thing you need to do is head over here and download a small update and run the file in order to let Windows Update download it. Here's the pertinent info from Microsoft:

The Windows Update Experience
Windows Vista SP1 RC requires the installation of either two or three prerequisite updates prior to installing the service pack itself. These prerequisite updates will be delivered to most users over Windows Update as part of regularly scheduled monthly updates prior to the release of the service pack. This will help ensure that reboots required by the prerequisite updates occur with other updates that require a reboot. However, because these prerequisite updates have not been released, installing Windows Vista SP1 RC will require 3 to 4 separate installations over Windows Update. Please note that the instructions below are primarily required for the RC installation and will not be required for most users using Windows Update to install the final Service Pack.
The prerequisite updates consist of two updates which service specific Windows components prior to the installation of the service pack and a third update which services the installation software built into Windows Vista. The following are the prerequisite updates.

• KB935509 This updates is only required on Windows Vista Enterprise and Windows Vista Ultimate editions (which have Bitlocker capabilities). This update is required prior to installing KB938371, the second prerequisite update and is required to prevent potential loss of data on Bitlocker encrypted systems during updating.
• KB938371 This update consists of fixes for several components (including the TrustedInstaller), increases the success rate for installing the service pack and enables the service pack to be uninstalled successfully.
• KB937287 This is an update to the “Servicing Stack” or the Windows Vista component installer technologies built into Windows Vista. This update enables the built-in installer to properly and successfully install the service pack.

Installing the Service Pack
There are two ways to install the service pack, first, as a pop-up notification that the service pack is ready to be installed (this is the method in which most users will install the service pack) and using multiple manual installations from Windows Update. The first method is the simplest, but may take up to four days for the Windows Update Automatic Update feature to deliver each of the 3 prerequisites and the service pack. Windows Vista SP1 distributed through Windows Update will be applicable to Windows Vista machines that are running on any of the 36 languages supported by Windows Vista RTM.
Method 1: Automatic Update
You can install Windows Vista SP1 RC using the Automatic Update process by following these steps.

1. Save the included SP1cppRK.cmd script to your machine.
2. Right-click on the script and select Run as administrator. The script will set a registry key on your machine that allows Windows Update to offer Windows Vista SP1 RC to your machine.
3. From the Windows Update control panel, select Change settings.
4. Verify that Install updates automatically (recommended) is selected. This enables the Automatic Update feature to download and install the prerequisite updates and service pack automatically.
5. Windows Update Automatic Update will automatically update your machine over the next several days with the prerequisites updates. When the service pack has downloaded a pop-up notification will inform you that updates are ready to be installed. You must click on this notification and choose to install the service pack at this point. The service pack will not silently or automatically install itself.

Method 2: Manual Installation using Windows Update
To install Windows Vista SP1 RC as quickly as possible, follow the steps below.

1. Save the included SP1cppRK.cmd script to your machine.
2. Right-click on the script and select Run as administrator. The script will set a registry key on your machine that allows Windows Update to offer Windows Vista SP1 RC to your machine.
3. Windows Update Automatic Update will automatically update your machine over the next several days with the prerequisites updates provided you have the Windows Update Automatic Update feature enabled. When the service pack has downloaded a pop-up notification will inform you that updates are ready to be installed. You must click on this notification and choose to install the service pack at this point. The service pack will not silently or automatically install itself.
4. To manually install the service pack, start by installing all Important updates applicable to your system and the prerequisite updates. You may have to repeat this several times to fully update your system by opening the Windows Update control panel and selecting Check for updates. Note: If your system is managed by a administrator and has a Windows Server Updates Services (WSUS) server for updates, you need to use the Check online for updates option of the Windows Update control panel. If this option is not available, your administrator may have disabled this functionality.
5. If you have Windows Vista Ultimate or Windows Vista Enterprise, Update for Windows Vista (KB935509) should be in this list. If you have any other version, Update for Windows Vista (KB938371) should be in this list. Install these updates and reboot your machine when prompted.
6. If you do not have Windows Vista Ultimate or Windows Vista Enterprise Update for Windows Vista (KB938371) should be in the list first and Update for Windows Vista (KB935509) is not required. Note: If you reboot and immediately check for updates you may not see all updates. This may be caused by the installer service completing the installation of the prior update. Please wait 5-10 minutes and check for updates again.
7. Install Update for Windows Vista (KB937287). Update for Windows Vista (KB937287) does not require a reboot.
8. Wait for 10-15 minutes before checking for updates again to enable the installer to complete its installation.
9. Check for updates again and install Service Pack for Windows (KB936330).