Image gallery scroller

I would like to create a vertical AS scroller to scroll through thumbnail images. I need to be able to view only 3 images at a time, visible through a mask window, though the clip containing the thumbnails could be much longer (10+). I want to be able to use the mouse coordinates (either above or below the mask window) to initiate the scrolling. However, the problem I am having so far is that all the code I found so far is based on a center point of the clip and requires only minimum movement in either direction to begin moving the images. I would like to be able to control that area and NOT have the images move until my cursor is OUTSIDE the mask window. Is there a way to do that without having to resort to invisible buttons? The beauty of the mouse coordinate system is that it allows for variable speed based on distance away from the center. Is there a way of extending that INACTIVE zone? Please help. Thanx.

georgia :puzzle:

PS. The code I am using here is from the book SKIP INTRO.