function sndReq(action) { 
    http.open('get', 'output.php?action='+action); 
    http.onreadystatechange = handleResponse; 
    http.send(null); 
}

<tr>
		<td><img id="index_11" src="http://xhtmlforum.de/images/index_11.png" width="2" height="418" alt="" /></td>
		<td>
        	<div id="smallbox" style="width:240px; height:418px; overflow:auto; border:0px;"></div>
		</td>
		<td><img id="index_13" src="http://xhtmlforum.de/images/index_13.png" width="2" height="418" alt="" /></td>
		<td colspan="7">
			<div id="bigbox" style="width:476px; height:418px; overflow:auto; border:0px;">
				<script type="text/javascript"> 
      			sndReq('getHome'); 
      			</script>

            </div>
		</td>
		<td><img id="index_15" src="http://xhtmlforum.de/images/index_15.png" width="2" height="418" alt="" /></td>
	</tr>

<a href="javascript:void(0);" onClick="sndReqBB('getProfilBB');sndReqSB('getProfilSB');"
            	onmouseover="MM_swapImage('Profil Button','','images/index_04ro.png',1);  window.status='Wer wir sind und was wir tun erfahren Sie hier...';  return true;"
				onmouseout="MM_swapImgRestore();  window.status='';  return true;"><img src="http://xhtmlforum.de/images/index_04.png" alt="Profil Button" name="Profil Button" width="61" height="41" border="0" id="Profil Button" />
</a>

function sndReqBB(action) { 
    http.open('get', 'bigboxout.php?action='+action); 
    http.onreadystatechange = handleResponse; 
    http.send(null); 
} 

function sndReqSB(action) { 
    http.open('get', 'smallboxout.php?action='+action); 
    http.onreadystatechange = handleResponse; 
    http.send(null); 
}

<?php
switch($_REQUEST['action']) {
  default:
  case 'getHomeSB':
    $filename = 'txt_home/text_smallbox.html';
    break;
  case 'getProfilSB':
    $filename = 'txt_profil/text_smallbox.html';
    break;
......usw.

}
$handle = fopen($filename, 'r');
$content = fread($handle, filesize($filename));
fclose ($handle);
echo 'smallbox|'.$content;
?>

<?php
switch($_REQUEST['action']) {
  default:
  case 'getHomeBB':
    $filename = 'txt_home/text_bigbox.html';
    break;
  case 'getProfilBB':
    $filename = 'txt_profil/text_bigbox.html';
    break;
.....usw.
}
$handle = fopen($filename, 'r');
$content = fread($handle, filesize($filename));
fclose ($handle);
echo 'bigbox|'.$content;
?>