Creating a real-time magnifier

[Richard Miller]

Any thoughts on how to magnify (by 2x) a 100x100 section of the screen 
in real time? I can't see how export snapshot could be used for this.... 
not in real time. Perhaps it involves manipulating screen/picture data, 
but I don't have the experience in doing this. I'd like the user to be 
able to move a 100x100 rectangle over the screen and have that section 
of the screen magnified to double and displayed in a rectangle in a corner.

Thanks for any suggestions.
Richard Miller