Rollover effects are fun in HTML but too much code and alternate images means your page takes longer to render in the browser. Don't forget that some effects are built into browsers. For example, there are pseudo-classes like :hover for the anchor tag. As you can see in the sample code, adding styles can change the background color of links as the mouse passes over.
<a href="#">Pass your cursor here.</a>
Other pseudo-classes include :active, :link and :visited.