Windows Vista Service Pack 1 (Generic Overview and entry point)
http://technet2.microsoft.com/WindowsVista/en/library/90a564b9-34af-4a6b-937f-324e1862244b1033.mspx?mfr=true

Some interesting topics out of the hole documentation: 

Overview of Windows Vista Service Pack 1
When developing Windows Vista, Microsoft set out to provide higher levels of productivity, mobility, and security, with lower costs. After more than six months of broad availability and usage, it’s evident that these investments are improving the Windows computing experience.
In addition to regular Windows Vista updates, application compatibility improvements, and device driver improvements, Windows Vista Service Pack 1 (SP1) is another way Microsoft will deliver improvements to the Windows Vista customer experience.
The goal of Windows Vista SP1 is to address key feedback Microsoft has received from its customers without regressing application compatibility. Windows Vista SP1 will deliver improvements and enhancements to existing features that significantly impact customers, but it does not deliver substantial new operating system features. For example, the service pack improves the performance of the desktop shell, but it does not provide a new search user interface or a new version of Windows® Media Center.
http://technet2.microsoft.com/WindowsVista/en/library/90a564b9-34af-4a6b-937f-324e1862244b1033.mspx?mfr=true

Hotfixes and Security Updates included in Windows Vista Service Pack 1
Windows Vista Service Pack 1 includes all previously released updates for Windows Vista. Many of these updates are available to the public on the Microsoft Download Center and Windows Update, while others are only available to specific customers or partners. It is standard practice to include all of these updates in a Service Pack and as such they are included in Windows Vista SP1.
http://technet2.microsoft.com/WindowsVista/en/library/90a564b9-34af-4a6b-937f-324e1862244b1033.mspx?mfr=true

Notable Changes in Windows Vista Service Pack 1
Microsoft continuously improves the Windows Vista Operating System by providing ongoing updates while working with software and hardware vendors to help them to deliver improved compatibility, reliability and performance. These updates are provided to customers directly by our hardware and software partners, as well as from Microsoft in the form of hotfixes distributed on a regular basis using Windows Update. Updates to Windows are also delivered directly to some affected customers and preinstalled by PC manufacturers.
http://technet2.microsoft.com/WindowsVista/en/library/90a564b9-34af-4a6b-937f-324e1862244b1033.mspx?mfr=true

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