function is_empty(field, text) {
	if($(field).value == '') {
		alert("Por favor introduzca su  '" + text + "'");
		return true;
	}
	return false;
}

function is_invalid_email(field, text) {
	 email = $(field).value
	 AtPos = email.indexOf("@");
	 StopPos = email.lastIndexOf(".");

	 if (AtPos == -1 || StopPos == -1) {
		alert("Por favor introduzca un E-mail válido");
		 return true;
	}
	return false;
}

/*
 * Switch between elements using a scriptaculous animation
 */
function swapel(el1, el2) {
	var duration = 0.3;  //Duration for Fade/Appear
	var el1 = $(el1);
	var el2 = $(el2);
	Effect.Fade(el1, {duration: duration, 
		afterFinish: function(){
			Effect.Appear(el2, {duration: duration})
		}
	});
}