1. Hype up your new operating system.
2. Announce that you will have a public beta within a month.
3. When you release the public beta, make sure you tell everyone it will only be available to a limited number of people for one day.
The Windows 7 beta is supposed to be available today. I’ve been trying for a while, but their system is so hammered I can’t get to the page where I’m supposed to get my product key and download link.