a 'mouseover' and your web design software will almost certainly do it for you. Tell me what you use, and I'll see if I can point you in the right direction.
When you see something on a web page that you want to know more about, click on the 'view' menu in Internet Explorer and select 'source'.
A new notepad window will appear, and in it will be all the HTML (and other) code that makes up the page. You might not understand it all, but it may provide a useful pointer - try it on the page in your link. Can you see the 'onMouseOver' references?