var table = 
    document.all ? // IE
      document.all['tableID'] :
    document.getElementById ? // NN6 or other DOM compliant browser
      document.getElementById('tableID') :
        null; // no access
and then you script table.rows for instance
  if (table) // browser supports TABLE access
    // use table.rows for instance color rows alternatingly
    for (var r = 0; r < table.rows.length; r++)
      if (r % 2 == 0)
        table.rows[r].bgColor = 'red';
      else
        table.rows[r].bgColor = 'green';