If it is really important for you, I think there is a workaround that would allow you to record a Windows Seven screensaver. This is just an idea, I have not tested it but it should work. it includes a bit more preparations but, as I said, if it is important for you it is doable.
Install any of the free virtualization applications, Virtual PC
or VMware Player
. Set up a Seven virtual machine, you can use your own install media and use Windows on vm a few days without activation. Only if you want to keep it do you need a valid license.
When installed, start your new Seven vm. Start your screen capture program, expand Seven vm to full screen, start screensaver. When enough, exit vm full screen, stop screen capture on host and that's it.
(*) Although Windows XP Mode is only available for Seven Pro or better, Virtual PC is available for every edition of Seven except Starter. See this post for installing Virtual PC on Home editions of Seven: Hey/Help