var IMAGE_PATH = "./images/navigation/";
var EXTENSION = ".jpg";
var HOVEREXT = "_hover";

function unhighlight(imgName)
 {
  
   if (document.images)
    {
    
      document.getElementById(imgName).src = IMAGE_PATH + imgName + EXTENSION
      
    }
 }

function highlight(imgName)
 {
   if (document.images)
    {
      document.getElementById(imgName).src = IMAGE_PATH + imgName + HOVEREXT + EXTENSION; 
    }
 }