Below is the html and CSS code to map an image. IE is a pain in the butt about letting us set the height of the link block without an image. So I am forcing the issue by added a blank image to the links. The image defines the height of the link area (which was just removed from the css). Make sure the links use a target of parent so that the links will leave the iframe wrapper (if you put this in an iframe, as I have below).

<style type="text/css">
.swine_flu_img { position: relative; width: 151px; height: 141px; background-image: url(http://pgale.web.unc.edu/?attachment_id=315); background-repeat: no-repeat; }
.link-1-Top { top: 34px; }
.link-2-Top { top: 53px; }
.link-3-Top { top: 72px; }
.link-4-Top { top: 90px; }
.linkBase { position: absolute; left: 20px; width: 110px; }
.linkHover:hover { opacity:0.2;filter:alpha(opacity=20); background-color: #fff; border: 1px dotted #fff; }
</style>
<div class="swine_flu_img">
<a class="linkHover linkBase link-1-Top" href="http://www.sph.unc.edu/swineflu#nc" title="N.C. Info" target="_parent"><img src="http://www.sph.unc.edu/images/blank.png" height="14px" border="0"></a>
<a class="linkHover linkBase link-2-Top" href="http://www.sph.unc.edu/swineflu#unc" title="UNC Info" target="_parent"><img src="http://www.sph.unc.edu/images/blank.png" height="14px" border="0"></a>
<a class="linkHover linkBase link-3-Top" href="http://www.sph.unc.edu/swineflu#school" title="School Info" target="_parent"><img src="http://www.sph.unc.edu/images/blank.png" height="14px" border="0"></a>
<a class="linkHover linkBase link-4-Top" href="http://www.sph.unc.edu/swineflu#news" title="In the News" target="_parent"><img src="http://www.sph.unc.edu/images/blank.png" height="14px" border="0"></a>
</div>