Here is a site that provides a javascript class that allows you to create the mouse over notes /tips that you might find on some Flickr images.

According to the site this should work on the following browsers: Internet Explorer 5.5+, Firefox 1.0+, Safari 2.0+, Opera 7.6+. Below are a few image examples of what the script allows you to do with your images.

Regular Image

Mouse Over (you can see the note boxes)

Roll Over Boxes (notes for that area is displayed)