Microsoft was confirming officially that the second service pack for Vista and Windows Server 2008 had indeed been made available to the public, after the bits were initially released to MSDN and TechNet subscribers the past week. SP2 for Vista is packaged both as an .EXE file, and as a standalone DVD ISO, but can additionally be accessed through Windows Update.
Windows Vista Service Pack 2 (SP2) Release Candidate (RC) and Windows Server 2008 Service Pack 2 (SP2) Release Candidate (RC) are available for download here.