var preloaded = [];

		// preload de menu
		for (var i = 1; i <= 4; i++) {
			preloaded[i] = [loadImage("boton_r1_c"+ i + ".gif"), loadImage("boton_r1_c"+ i + "_f2.gif")];
		}
		for (var i = 1; i <= 3; i++) {
			preloaded[i+4] = [loadImage("iconos_nav_diputacion_r1_c"+ i + ".gif"), loadImage("iconos_nav_diputacion_r1_c"+ i + "_f2.gif")];
		}
		function init() {
			// versiones de onload
			//==========================================================================================
			if (mtDropDown.isSupported()) {
				mtDropDown.initialize();

				menu1.onactivate = function() { swapImage("button1", preloaded[1][1].src) };
				menu1.ondeactivate = function() { swapImage("button1", preloaded[1][0].src) };

				menu2.onactivate = function() { swapImage("button2", preloaded[2][1].src) };
				menu2.ondeactivate = function() { swapImage("button2", preloaded[2][0].src) };

				menu3.onactivate = function() { swapImage("button3", preloaded[3][1].src) };
				menu3.ondeactivate = function() { swapImage("button3", preloaded[3][0].src) };

				menu4.onactivate = function() { swapImage("button4", preloaded[4][1].src) };
				menu4.ondeactivate = function() { swapImage("button4", preloaded[4][0].src) };

			}
		}

		// preloader numero 2
		function loadImage(sFilename) {
			var img = new Image();
			img.src ="nav/" + sFilename;
			return img;
		}

		// llamada al cambio de imagen
		function swapImage(imgName, sFilename) {
			document.images[imgName].src = sFilename;
		}