After playing more with the files Stampot generates, I figured out how its sprite track is triggering the hand cursor (letting the viewer know the poster movie is clickable).
The sprite track in Stampot poster movies links to an XML file called Stamp.xml, which in turn references the main movie. This XML file has the syntax
Using QuickTime Pro, I could extract the sprite track from the poster movie Stampot generated, paste it into another movie (using QT Pro's Add to Selection and Scale command), resize it to that movie's dimensions, and get a movie that generates a hand cursor. By then editing the XML file to point to another movie, I had what I wanted.
Of course, that's not a really practical solution because of all the steps involved. And although the sprite track can be reused in any movie, the intermediate XML file must always be named Stamp.xml.
Still, I satisfied my curiosity about how the heck Stampot was producing poster movies with a true hand cursor. If you design sites with QuickTime videos, Stampot is well worth the 20 bucks (15 Euros). More examples and a trial download here: www.qtbridge.com/stampot/stampot.html