Here is an example on how to set the attribute string id="header" for the thead tag. For the other two tags the procedure is similar.

$table = new HTML_Table();
// [...]
$thead =& $table->getHeader();
$thead->setAttributes(array('id' => 'header'));
// [...]
$table->display();

This would give the following result:

<table>
  <thead id="header">
    [...]
  </thead>
  [...]
</table>

Besides the possibility to pass attributes to the HTML_Table constructor, there are several more methods that can be used.

HTML_Table extends HTML_Common which offers methods like setAttributes() or updateAttributes(). A complete list of methods provided by HTML_Common can be found in its API documentation.