Looks like the Vista SP1 update for 64 bit users was a bit of a mistake....although it was the RTM version.
"A build of SP1 was posted to Windows Update and it was inadvertently made available to a broad group," Microsoft said in a statement. "The build was intended only for our more technically advanced testers, and was meant to only be offered to those with a specific registry key set on their PC. For general availability, we are still planning to make SP1 broadly available in the mid-March timeframe."
Full article here:
http://www.news.com/8301-13860_3-9876775-56.html?part=rss&subj=news&tag=2547-1_3-0-20