You may have seen this already bouncing around the interwebs thanks to a few nice people who leaked it outside of MSDN and Technet. Well now you can download it from the source rather than torrent that file. The link below takes you to the download page for the Vista SP1 RC1 files. Be aware that you might encounter a wierd flash like box when you go there. I did and it really played with my focus for a bit..
Update: The Super Site Blog has better links to stand alone installers for both 32 and 64 bit editions of Vista.