All you have to do is add "OnMouseOver" tag (or event) to your anchor in the following format:
OnMouseOver = "window.status='description'; return true;"
For example, if your original anchor tag looks like:
<A href="/home.html">
change it to:
<A href="/home.html" OnMouseOver="window.status='Go to my home page...'; return true;">
NOTE: Since OnMouseOver is a JavaScript event, your description will only appear on JavaScript enabled browsers such as Netscape 2.x+ and Explorer 3.x. Other browsers will simply ignore this tag.