For a very limited time only, Microsoft is offering an edition of Windows Vista prerelease RC1 on the Internet. The catch? You must have already signed up for the beta 1 release program back in June, and this new offer will end after the first 100,000 copies have been downloaded. The new version, build 5536, is not for the average user; it requires that you first download, then burn the ISO image onto a CD from which you may then install the new operating system. Microsoft is expected to offer an actual Release Candidate 1 build to the general public by the end of September 2006.