Drawing Board

I need to know how to script the drawing board as in the user can only draw on a specified area.For example, on a 800x600 layout, only 1/4 of it is the drawing board.After the user has drawn the image, when he/she clicks on a button, the image will be replicated on another area in the same 800x600 space.
So far, i can only manage to make a drawing board on the whole 800x600 space and erasing. Seriously need help…