function imgOn(imgName) {
        if (document.images) {
            document.desc.src = eval("nav_desc_" + imgName + "_on.src");         
						}
}

function imgOff(imgName) {
        if (document.images) {
            document.desc.src = eval("nav_desc_" + imgName + "_off.src"); 
						      
				}
}