Right now with 4.5 you can create iOS applications by creating an ActionScript mobile project. The 4.5.1 update due out in June is probably the functionality you are seeing in the videos.
Hit the BlackBerry site and download the Tablet OS SDK.
Once you've installed that, the BlackBerry PlayBook options will come up when you go to create a new mobile project. As for the iOS, if you poke around on the adobe site, I believe there's an air 2.6 SDK you can somehow install. Not sure yet, but I figure at least I could point you in the right direction for the PlayBook stuff.
Anyone knows when we can expect the "June" update?
Flashbuilder 4.5.1 was released today.