At the moment Service Pack 1 for Vista is still something officially unannounced. They are asking hardware vendors for drivers (see below) which would indicate an announcement may not be too far off.

General statements regarding the timeline for release have stated "second half of 2007".There has also been speculation that the release of SP1 will likely coincide with the release of Longhorn Server. Industry analysts suggest that fall of 2008 may be more realistic. In the mean time all critical updates are delivered via Windows Update so there really is no reason to get too worked up about just when it will come.

Recently Microsoft would appear to have starting the ball rolling when they
issued a call to hardware vendors for their latest device drivers. According to Microsoft, Vista natively supports 1.9 million devices. I'd love to see how they came up with that! (for the PC Magazine article click here).

Naturally, Vista Service Pack 1 will contain all of the security updates, hotfixes released to date, but it is also said to include other changes (with a focus on improving quality).