ขอคำแนะนำเกี่ยวกับ Ajax และการทำงานของ Span ที่มีหลายๆค่าค่ะ

<script language="JavaScript">
	   var HttPRequest = false;

	   function check() {
		  HttPRequest = false;
                  test = false;
		  if (window.XMLHttpRequest) { // Mozilla, Safari,...
			 HttPRequest = new XMLHttpRequest();
			 if (HttPRequest.overrideMimeType) {
				HttPRequest.overrideMimeType('text/html');
			 }
		  } else if (window.ActiveXObject) { // IE
			 try {
				HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
			 } catch (e) {
				try {
				   HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e) {}
			 }
		  }

		  if (!HttPRequest) {
			 alert('Cannot create XMLHTTP instance');
			 return false;
		  }

		  var url = 'preupload_check.php';
		  var pmeters = "tUsername=" + encodeURI( document.getElementById("filename").value);

                        HttPRequest.open('POST',url,true);

			HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
			HttPRequest.setRequestHeader("Content-length", pmeters.length);
			HttPRequest.setRequestHeader("Connection", "close");
			HttPRequest.send(pmeters);


			HttPRequest.onreadystatechange = function()
			{

				if(HttPRequest.readyState == 3)  // Loading Request
				{
					document.getElementById("mySpan").innerHTML = "";
				}

				if(HttPRequest.readyState == 4) // Return Request
				{
					if(HttPRequest.responseText == 'yes')

					document.getElementById('upload').disabled = true;
                                }
                                else
                                    {
                                        document.getElementById('upload').disabled = false;
                                    }

                        }


                 }
		</script>
 <table width="600" border="0" cellspacing="0" cellpadding="0">
<?
@session_start();
@$_SESSION['username']="$username";
?>        </p>
 <p>&nbsp; </p>
        <p> <span class="style5">
     <?
echo"<b>Login as : $username</b>";
?>
<? $time = date("Y-m-d");?>
            <? $gettime = date("H:i:s");?>
            </span></p>
   <table width="532"  align="center" >
          <tr>
            <td align="left" valign="top" class="mainContent" >
                <form method="post" action ="nusr_upload1.php" enctype="multipart/form-data">
              <div align="center">
                    <tr>
                      <td><p align="left" class="style2">ไฟล์อ้างอิง
                    <input type="text" name="filename" id="filename" OnChange="JavaScript:check();"/>
              <span id="mySpan"></span></div>
<input name="btnRegister" type="button" id="btnRegister" value="ตรวจสอบ"></input>
                        <input type="hidden" name="MAX_FILE_SIZE" value="5000000" />
                           <input name="userfile" type="file" id="userfile" />
                    <input name="upload" type="submit" class="box" id="upload" value="ทำการอัพโหลดไฟล์" />
 </form></td>
                    </tr>
</table>
           

<script language="JavaScript">
	   var HttPRequest = false;

	   function reLoad (url) {
		  HttPRequest = false;
		  if (window.XMLHttpRequest) { // Mozilla, Safari,...
			 HttPRequest = new XMLHttpRequest();
			 if (HttPRequest.overrideMimeType) {
				HttPRequest.overrideMimeType('text/html');
			 }
		  } else if (window.ActiveXObject) { // IE
			 try {
				HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
			 } catch (e) {
				try {
				   HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e) {}
			 }
		  }

		  if (!HttPRequest) {
			 alert('Cannot create XMLHTTP instance');
			 return false;
		  }

		    var pmeters = "";

			HttPRequest.open('POST',url,true);

			HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
			HttPRequest.setRequestHeader("Content-length", pmeters.length);
			HttPRequest.setRequestHeader("Connection", "close");
			HttPRequest.send(pmeters);


			HttPRequest.onreadystatechange = function()
			{

				 if(HttPRequest.readyState == 3)  // Loading Request
				  {
				   document.getElementById("mySpan2").innerHTML = "Now is Loading...";
				  }

				 if(HttPRequest.readyState == 4) // Return Request
				  {
					  document.getElementById('mySpan2').innerHTML = HttPRequest.responseText;
				  }
			}

	   }
	</script>
</head>
    <body Onload="JavaScript:reLoad('test.php');">
<div align ="center"><table width="1050" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td width="150" valign="top" align="center"><a href="JavaScript:reLoad('test.php');">หนัาหลัก</a></td>
    <td width="150" valign="top" align="center"><a href="JavaScript:reLoad('verificationx.php');">ตรวจสอบลายมือชื่อ</a></td>
    <td width="150" valign="top" align="center"><a href="JavaScript:reLoad('u_setting.php');">แก้ไขข้อมูล</a></td>
    <td width="150" valign="top" align="center"><a href="JavaScript:reLoad('popup_register.php');">ลงทะเบียน</a></td>
    <td width="150" valign="top" align="center"><a href="JavaScript:reLoad('preupload_search.php');">แสดงไฟล์</a></td>
    <td width="150" valign="top" align="center"><a href="index.html">ออกจากระบบ</a></td>

  </tr>

  <tr>
    <td colspan="4" valign="top"><span id="mySpan2"></span></td>
  </tr>
    </table></div>
    </body>
</html>