function ObtenerObjeto(str_id) {
      if ( document.all ) { //IE 4, 5, 6º
        return eval( "document.all."+str_id);
      }else if ( document.layers ) { //NETSCAPE 4
        return document.layers[ str_id ];
      }else if ( document.getElementById ) {
        return document.getElementById( str_id );
      }
}