mutiple boxes highlighted for a single mouseover

Hi,
I am trying to highlight multiple boxes(or areas) in the map of the world when the user mouses over a given weather model. For example, when the user mouses over a tab called “global Forecast system(GFS)”, the various regions of the world that are covered by this model should be highlighted on the map of the world. i.e NAmerica, SAmerica, Africa etc.
Here is the piece of code that i’m using.

<script language=”Javascript” type=”text/javascript”>
function show_tab(nam)
{
document.getElementById(“TABncoworld”).style.display= “none”;
document.getElementById(“TABnamerica”).style.display= “none”;
document.getElementById(“TABsamerica”).style.display= “none”;
document.getElementById(“TABafrica”).style.display= “none”;
document.getElementById(“TABcanada”).style.display= “none”;
document.getElementById(“TABnpacific”).style.display= “none”;
document.getElementById(“TABepacific”).style.display= “none”;
document.getElementById(“TABnwatlantic”).style.display= “none”;
document.getElementById(“TABpolaricedrift”).style.display= “none”;
document.getElementById(“TABatlanticpacific”).style.display= “none”;
document.getElementById(nam).style.display = “block”;
}
</script>

<td width=”107″ class=”nav” id=”menuitem”><div align=”center” style=”font-size: xx-small; font-weight: bold”><a href=”http://www.spc.noaa.gov/products/outlook/” class=”style3″ onMouseOver=”show_tab(‘TABnamerica’)”>NAM</a></div></td>
<td width=”107″ class=”nav” id=”menuitem”><div align=”center” style=”font-size: xx-small; font-weight: bold”><a href=”http://www.spc.noaa.gov/products/outlook/” class=”style3″ onMouseOver=”show_tab(‘TABnamerica’);show_tab(‘TABsamerica’);show_tab(‘TABafrica’)” alt=”Current Day 1 Outlook”>GFS</a></div></td>

When I mouse over ‘GFS’, both TABnamerica and TABsamerica should get selected. But only TABsamerica shows. I want all the boxes to be highlighted. how do i fix this?

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