It sounds like you're tring to do something like sprites; where you have just one image loaded and then move the "view port" around to show different images.
If that's the case, you won't be able to do this with the stock PictureBox class. You can control the sizing, but not the positioning. I think what you'd have to do is load the image, via code, and create new images based off the necessary portion of that image (using GDI+).