For the record, the "alt" parameter of an <img> tag only shows up as hover text in IE. W3C specs are the "title" parameter should be used for hover text. The "alt" parameter is for displaying text should the img be broken for whatever reason.
The reason I point this out is more modern W3C compliant browsers such as Firefox will not show "alt" text as hover text. IE does it wrong and sucks, basically. Bottom line, always include "alt" and "title" parameters on images.