That's because there is no installer yet. It's just a file which you can put anywhere on your computer. If you put it in the proper directory (I don't remember which it would be for Vista 64 - something extremely counter-intuitive), then it will always show up in the list. If you set it as your screensaver by right-clicking the file and selecting "Install", then later choose "None", you will have to do the same thing all over again.
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