Service Pack 2 for Vista not being shown in windows update

Im running Vista SP1 with all latest updates from windows updates on a Dell Studio 1555 laptop. But SP2 isn't in the windows update at all. It keeps saying Im up to date

You can download sp2 for Vista from Microsoft website.

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=a4dd31d5-f907-4406-9012-a5c3199ea2b3