Windows Vista SP1 release candidate available for download
You're probably better off going through Windows Update, as Vista will just install the packages that you need. But you may have to check for updates and reboot several times before you actually get SP1.
We're still test driving our copy of Vista SP1 RC, but we've been hearing so much about this update over the last few months that we almost feel like the magic wore off before it was even released. While there are a ton of bug fixes, reliability, and compatibility enhancements in Windows Vista SP1, users shouldn't expect a major performance boost.
Bear in mind, this is a release candidate, not a final release. That means Microsoft could still make some changes before pushing Service Pack 1 out to all customers early next year. It also means that if you don't want to be a glorified beta tester (we know, a release candidate is more stable than a beta, but no one ever talks about "release candidate testers") you might want to hold off on downloading SP1 RC. For a little while at least.