Windows Vista SP1 is now downloadable via Windows Update.  Get the full story from Nick on the Vista Team Blog.

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Get the x86 standalone package @ http://www.microsoft.com/downloads/details.aspx?FamilyID=b0c7136d-5ebb-413b-89c9-cb3d06d12674&DisplayLang=en.

Get the x64 standalone package @ http://www.microsoft.com/downloads/details.aspx?FamilyID=874a414b-32b2-41cc-bd8b-d71eda5ec07c&DisplayLang=en.