Windows Vista SP1 Update Available via Microsoft OEM site
It looks like Microsoft has posted the final Vista SP1 bits to their OEM site which is accessible to anyone that registers. The file is a 1.13GB .img which combines the 32-bit and 64-bit update executables into one image:
Windows Vista Service Pack 1 (SP1) is now available for download. Windows Vista SP1 will deliver improvements and enhancements to existing features that significantly impact customers, but it does not deliver substantial new operating system features.
Download Windows Vista SP1 here. The download contains Window Vista SP1 for five languages: English, French, German, Japanese, and Spanish. Note Additional languages will be available soon.
Once you download the Windows Vista SP1 package, you will need to extract the appropriate .exe file for the language you wish to install.
Download: Windows Vista SP1 Update Image (32-Bit & 64-Bit)