I downloaded Photoshop CS6, and Adobe download assistant said it was the Extended edition, but I don't see the word "Extended" in the about box.
Should I have access to "Stacks Mode"? If so, how can I find it?
Works for me in CS5.5 and CS6 Beta, but I don't have the full CS6 yet.
Have you converted to a Smart Object first? Layers/Smart Objects/Convert to Smart Object. The only reason the Stack Mode would be disabled that I can think of, is if the selected layer is not a smart object.
In my CS6, in the about box I see "EXTENDED" in small, light blue type far to the right in the top.
For stacks in Photoshop, go to File > Scripts > Load Files into Stack...
Bridge should have a Stacks main menu item.
Somewhat depends on what type of Stacks you're looking for.