With Dynamic HTML and Internet Explorer 4 and 5 you can update the text on the page after the page is rendered. The trick is to use the ID attribute as a unique identifier for the tag. As the user rolls the cursor over the text, the onmouseover event replaces the text between the opening and closing tags. Here's a short example:
onmouseover="mytext.innerText='Longer description of the same item using DHTML for IE.';">
You can restore the original text by including it as part of the onmouseout event.