When using Column View in the Finder, holding the Option key while clicking the preview of an image will zoom the image. Holding Shift-Option while clicking zooms out the image.
Click and drag in a zoomed image pans the image. I discovered this by accident when holding the option key while dragging the preview image during a copy. I mistimed the keypress and mouse click and instead zoomed the image.
[crarko adds: I tested this, and it works as described. This appears to be Snow Leopard only.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20101120063903301