Yesterday I promised the stand alone update would be coming soon. I just checked and the 32-bit version is now available on the Microsoft Volume License Services website (MVLS). I am expecting the 64-bit version to follow soon. I’ll amend this post when I confirm it is online as well.
If you want to make sure you have the correct download, look for "Patch" in the title of the ISO. This ensures it is the update to apply SP1 to an existing RTM machine, not a slipstreamed version of the OS install DVD.
I am told this will work for all versions of Vista. If you find otherwise, please let me know and I will update this post. I run Enterprise on my laptop so I don’t have anything handy to test it on Ultimate.