function preloadImages() {
		  if (document.images) {
		    var imgFiles = preloadImages.arguments;
			var preloadArray = new Array();
			for (var i=0; i<imgFiles.length; i++) {
			preloadArray[i] = new Image;
			preloadArray[i].src = imgFiles[i];
		    }
		  }
		}

		preloadImages('images/but1_off.gif');
		preloadImages('images/but2_off.gif');
		preloadImages('images/but3_off.gif');
		preloadImages('images/but4_off.gif');
		preloadImages('images/but5_off.gif');
		preloadImages('images/but1_on.gif');
		preloadImages('images/but2_on.gif');
		preloadImages('images/but3_on.gif');
		preloadImages('images/but5_on.gif');

		// set button on/off
		var flag = 0;			//global variable
		function setButton(id) {
			if (id == "") return;
 
			if(document.body.id != 0) {
				if (eval('document.images["but' + document.body.id + '"]').src != eval('document.images["' + id + '"]').src)
					setImg(id); 
				}
			else
				setImg(id);
			}

		// set the right image
		function setImg(id) {
			if (flag == 0) {
				eval('document.images["' + id + '"]').src='images/' + id + '_on.gif';
				flag = 1;
			}
			else {
				eval('document.images["' + id + '"]').src='images/' + id + '_off.gif';
				flag = 0
			}
		}

		function setPage() {
			var id = document.body.id
			if(id != 0)
				eval('document.images["but' + id + '"]').src='images/but' + id + '_on.gif';
		}