function serializar(formulario){
	var i, j
	var cadena = ""
	var valor = ""
	for (i=0;i<formulario.length;i++){
		if(formulario[i].type == "checkbox"){ // checkbox
			valor = ""
			if (formulario[i].checked){
				valor = formulario[i].value
				cadena +=  formulario[i].name+"="+escape(valor)+"&"
			}
		}
		else if (formulario[i].type == "radio"){ // radiobutton
			if (formulario[i].checked){
				valor = formulario[i].value
				cadena +=  formulario[i].name+"="+escape(valor)+"&"
			}
		}
		else // resto de tipos de campos
			cadena +=  formulario[i].name+"="+escape(formulario[i].value)+"&"
	}
	return(cadena)
}