In this context, SP1 would have to be installed on top of the operating system after Vista was deployed on a machine.
The alternative is to have both Vista RTM and Vista SP1 RTM as two standalone products. A slipstream version of Windows Vista Service Pack 1 is essentially nothing more than the RTM version of the latest Windows client with the service pack already integrated. Microsoft is offering for download both the 32-bit and 64-bit Windows Vista SP1, the slipstream versions as ISO images.
