Awhile ago i found a tut on masking. i cant remember where i saw it…so maybe someone here does. Or even better someone can tell me how to do it 
I’ll do my best to describe what im looking for.
Pretend we have two layers. on the bottem layer we have an image and on the top layer we have a white box covering the entire image on the below layer. When someone drags their mouse over the top layer it erases the white (when you click and hold)revealing the image underneath.
does this ring a bell with anyone?
I really need this and im totally screwed because i havent the foggiest on how to achieve this goal.
thanks.
