Well with a link you can do this:
a
{
color: black;
}
a:hover
{
color: red;
}
When you hover your mouse over a link it goes from black to red. And you can do bold, underline, and multiple other things in there. If there is a "div:hover" you can do it with CSS, which would be far better than JavaScript. But I'm not sure if div has a hover property in CSS :S.