function rollover(){
			var source = this.src.toString();
			var srcRoot = source.substr(0, source.length - 4);
			var newSrc = srcRoot + '-over.png';
			this.src = newSrc;
			this.onmouseout = function(){
				this.src = source;
				}
			}
		function navBarInitializer(){
			var btns = document.getElementById('topNav').getElementsByTagName('img');
			for(var i=0; i<btns.length; i++){
				
				addEvent( btns[i], 'mouseover', rollover);
				
				}
			}