Hmm. I'm using IE, but it doesn't do it for me. EDIT: It works if I enable Compatibility View. Thanks.
Tip: The alt attribute is meant to be used as an alternative text if the image is not available, not as a mouse-over text. To show a mouse-over text on images or image-maps, use the title attribute, like this: <img src="angry.gif" alt="Angry face" title="Angry face" />