As promised here is an example file how to use Multitouch Pinching to zoom in/out using the ScreenZoom object.
There are two frames, one that shows a combined drag/drop scrolling with zooming + scroll-speed altering based on scale and one frame that just shows the very basics (if you have trouble understanding the first more advanced frame).
When zooming in, you cant scroll entirely to the edges. This is a limitation that is pretty hard to work around.
You might be able to do it manually by setting the layer position itself when it can't scroll any longer due to the frame edges.