If you have Windows XP, do this:
Save the image to disk (right click, choose save as).
If you double click it, you should go straight to the 'Windows Picture and Fax Viewer' - there will be a row of buttons at the bottom (the first two are 2 blue arrows, then a few with a projector screen, then a couple with magnifying glasses, one +, one -). If you don't end up here, right click the saved image, and choose 'preview'.
You can now use those + and - keys to zoom in and out - once you've clicked the + you'll be given the ability to click anywhere on the image, and zoom in that section.
If you have a middle mouse button, or button a scroll wheel, you can press and hold that over the image to get a little hand, which will allow you to move the image around. Otherwise, you can use the scroll bars at the right and bottom of the image.
PLEASE NOTE! As the picture is so big, unless you have a very powerful computer zooming and moving can be a little bit slow - just have some patience