Today it is officially released to RTM, but wont be at Windows Update or Microsoft's website for download until mid-March at the earliest.
http://windowsvistablog.com/blogs/windowsvista/archive/2008/02/04/announcing-the-rtm-of-windows-vista-sp1.aspx
http://windowsvistablog.com/blogs/windowsvista/archive/2008/02/04/announcing-the-rtm-of-windows-vista-sp1.aspx