Microsoft released Service Pack 1 to the public today and it should be available via Windows Update soon for most people as well. However, if your looking to install the stand alone update of Service Pack 1 for Windows Vista 32 or Windows Vista 64, you can find it at the following Official Microsoft links. Hopefully, the service pack addresses the slow performance issues many have complained about in the past.
Windows Vista Service Pack 1:
Stand alone Official Download links: