function trataMarca()
{
  subcat = document.forms[0].marca;
  subcat.options.length = 0;
  subcat.options[0] = new Option("Carregando...","teste");
  if (ajax.readyState == 4) {
    subcat.options.length = 0;
    
   results = ajax.responseText.split(",");
    subcat.options[0] = new Option( "Selecione", "selecione" );
   for( i = 0 ; i < results.length; i++)
    { 
      string = results[i].split( "|" );
      subcat.options[1+i] = new Option( string[0], string[1] );
         
   } 
  }
}

function trataModelo()
{
  subcat = document.forms[0].modelo;
  subcat.options.length = 0;
  subcat.options[0] = new Option( "Carregando..", "selecione" );
  if (ajax.readyState == 4) {
    subcat.options.length = 0;
    results = ajax.responseText.split(",");
    subcat.options[0] = new Option( "Selecione", "selecione" );
   for( i = 0 ; i < results.length; i++)
    { 
      string = results[i].split( "|" );
      subcat.options[1+i] = new Option( string[0], string[1] );
         
   } 
  }
}