The System Preparation tool removes all collected WinSAT data in Windows Vista, and you cannot shorten the OOBE process by running WinSAT before the image is sealed
In Windows Vista, system assessment information is collected by the Windows System Assessment Tool (WinSAT) during the Out Of Box Experience (OOBE) process. This behavior leads to an increase in OOBE time.
To reduce the OOBE time in Windows Vista, you may want to run the WinSAT before the image is sealed. For example, you may want to run the WinSAT in the factory. However, if you run the WinSAT before the image is sealed, all the WinSAT data that is collected cannot be preserved when you reseal the image. Therefore, you cannot reduce the OOBE time by running WinSAT during the image preparation phase.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB958011.