First, I'd suggest the image control instead of the picture box.
1) Put a frame with no border on your form.
2) Place an image inside the frame.
3) Set the imagecontrols "stretch" property to TRUE.
3) When the user clicks the button, enlarage the imagecontrol, and set it's "top" and "left" properties so it shows the correct part of the picture.

Should work...

//Anders