Get it from http://www.microsoft.com/downloads/details.aspx?FamilyID=b0c7136d-5ebb-413b-89c9-cb3d06d12674&DisplayLang=en.
I had the RC1 installed and so when i tried installing the SP1 release then it gave me an error that SP1 is already installed.
So, you must remove all previous version of SP1 before upgrading to the next.
Control Panel > Programs and Features > Installed Updates (upper left corner
under Tasks) > Highlight "Service Pack KB936330" > Uninstall
It will take awhile, there will be 2-3 reboots. Then you can install the
Follow the above steps and then go to the given link above (for MS download center for Vista SP1) and download and install the SP1 here. To know the features of SP1 please refer to this article.