Vista Service Pack 2, which will include all previously included updates, is coming soon. It had been in beta or testing for a while. In other words, the brave (foolhardy?) were able to try it, if desired. This is essentially being a guinea pig for Microsoft, but hey, someone has to do it. Anyway, at this point in time (May 1st, 2009) the official release of SP2 is not available.
"Service Pack 2 (SP2) for Windows Server 2008 and Windows Vista is an upcoming update to Windows Vista and Windows Server 2008. It will provide customer and partner feedback-driven fixes into a single service pack, minimizing deployment and testing complexity. In addition to all previously released updates since SP1, SP2 will support new types of hardware, and will add support for several emerging standards.
As of April 28th, 2009 the Windows Server 2008 SP2 and Windows Vista SP2 Beta program has concluded, thank you for your participation and feedback.
This site will be updated to include Service Pack 2 download details when they are available." This Technet site has all updates: