x = "images/nav_"

if (document.images) {            
 
insideon = new Image();  insideon.src = x + "inside_mo.jpg";
marketson = new Image();  marketson.src = x + "markets_mo.jpg";
serviceson = new Image();  serviceson.src = x + "services_mo.jpg";
sitemapon = new Image();  sitemapon.src = x + "sitemap_mo.jpg";
 
insideoff = new Image();  insideoff.src = x + "inside_on.jpg";
marketsoff = new Image();  marketsoff.src = x + "markets_on.jpg";
servicesoff = new Image();  servicesoff.src = x + "services_on.jpg";
sitemapoff = new Image();  sitemapoff.src = x + "sitemap_on.jpg";

        }
    function imgOn(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "on.src");       
            }
    }
    function imgOff(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "off.src");        
            }
           
    }