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i don't think you're going to get any help here since there is no public beta of Leopard and talking about it is probably a violation of the NDA you signed (assuming it's a legit copy of Leopard, which i'm sure it is).
 
I don't have a copy, or an NDA to break so here goes:

1) Perhaps you can't?

2) Perhaps you can use the shortcut key to invoke it for whatever item the mouse is over?
 
Well, as I said I was just curious. They show the tiled vertical stacks as well as the QuickView option in the videos I've seen.
 
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