In my excitement and pre-caffeinated state, I missed something about Photosynth that should have been spectacularly obvious:
You can only run it on MS Vista or XP SP2. Even just the test drive.
Now, I am conflicted, to say the least. I've read about the somewhat broken nature of Vista, in terms of overenthusiastic security and DRM-type restrictions, but I haven't actually tried it out. I guess I'll just move into wait-and-see mode on Photosynth and its worthiness as a product. My institution is a Windows house, so it's probable that I'll get to play with it sooner rather than later.
It's frustrating, nonetheless. A cool tool, but of limited use to someone unwilling to buy (into) the OS.