I had an example on my N900 with stackable windows working with PyQt/PySide, but my N900 is in for repair and I didn't back up the information.

At any rate, I thought you might find the documentation helpful. (note the URL). This includes all of the maemo-specific classes of Qt 4.6, and a lot of them should easily translate to python. For Stacked Windows in particular, see this example.

In summary, I believe that the stacked window (the one that should have an arrow instead of an x) should be a child of the main window, and all should set the stacked window property.