[Osiris]

The registry tweaks to download previous versions Windows Vista Service Pack 1 do not longer have the desired results because Microsoft is already distributing the release candidate 1 of Windows Vista SP1 using Windows Update. The old keys that have been added to the Registry previously have to be removed and new keys have to be added.
The release candidate of Windows Vista Service Pack 1 should then be available via Windows Update. It might be that you will have to download some prior updates before the Release Candidate becomes available. It should be noted that this is only working on English editions of Windows Vista unless you tweak the Registry on non-English Vista editions to make Vista believe that you are using an English Vista.
Download the file Windows Vista Service Pack 1 Hack and unpack it to your Vista system. Executing the file will remove the old Registry keys that are no longer needed and add the new ones.
Another option would be to open the file in a text editor and manually remove and add the keys to the registry. Restart your computer afterwards and visit Windows Update. You will most likely be prompted to install three minor updates before you will see the Windows Vista Service Pack 1 in the list, those are:

• Update for Windows Vista (KB935509) - v1.008
• Update for Windows Vista (KB938371) - v1.028
• Update for Windows vista (KB937287) - Build 6001.17052

Make sure you restart your computer after each update even though you will not get a prompt to do that.
Now you will see Windows Vista Service Pack 1 Release Candidate 1 - Build 6001.17052 in the update list. Download and install it normally to update your system to Service Pack 1.
via My Digital Life