//funcion para validar numeros en los txt
var nav4 = window.Event ? true : false;
	function acceptNum(evt)
	{	// NOTE: Backspace = 8, Enter = 13, '0' = 48, '9' = 57	
		var key = nav4 ? evt.which : evt.keyCode;	
		return (key <= 13 || (key >= 48 && key <= 57));
	}
//<input type="text" class='f12n' name="Txt_Cant" maxlength="3" size="3" value="0" onKeyPress="return acceptNum(event)">