function addLoadEvent(func) {
    var oldonload = window.onload;
    if (typeof window.onload != 'function') {
        window.onload = func;
    } else {
        window.onload = function() {
            if (oldonload) {
                oldonload();
            }
            func();
        }
    }
}

addLoadEvent(function() {

			var navroot = document.getElementById('dropdownmenu');
			var imgs=navroot.getElementsByTagName("IMG"); 

			for (i=0; i<imgs.length; i++) {

				imgs[i].onmouseover=function() {
					this.src = this.src.replace(".gif","_over.gif");
				}
				imgs[i].onmouseout=function() {
					this.src = this.src.replace("_over.gif",".gif");
				}
			}


})