In the example given there is a variable called $html, well to personalise the message you would modify this variable: e.g. Your form sent a variable called $name
As you can see from the example to add an image you do the following:
$html = '<HTML><BODY BACKGROUND="background.gif">'."\r\n".'<FONT FACE="Verdana, Arial" COLOR="#FF0000">'."\r\n".'Hello '.$name.' how are you today.</FONT>'."\r\n".'<P></BODY></HTML>';
$filename = 'yourimage.gif';
$image = fread($fp = fopen($filename, 'r'), filesize($filename));
note that you must change the image/gif to the appropriate mime type for the image format used.
$mail->add_html_image($image, 'yourimage.gif', 'image/gif');
If you need any more help then I will see if I can come up with a clearer example.