Opdatering af billeder udfra feltnavn

Jeg skal med følgende metode:

<!-- UDF Used to update the progressbar -->
function UpdateProgressBar(blockFrom, blockTo, percentDone, currentTask) {
    var insBlock;
   
    document.statusForm.progressbarPercent.value = percentDone;
    document.statusForm.progressbar.value = currentTask;
   
    for(; blockFrom <= blockTo; blockFrom++) {
        insBlock = "Block"+blockFrom;
        document.statusForm.getElementById('insBlock').src = "frames/gfx/progressbar_green.jpg";
    }
}

Opdatere billedet Block#nummer# på følgende side:

<form action="" name="statusForm" id="statusForm">
<table width="100%" border="0" cellspacing="0" cellpadding="0" height="100%">
  <tr>
    <td align="center">
      <table width="302" border="0" cellspacing="0" cellpadding="0" height="140" background="frames/gfx/progressbar_bg.jpg">
        <tr>
          <td height="26" colspan="2">&nbsp;</td>
        </tr>
        <tr>
          <td height="30">&nbsp;<span class="progressbarTekst">Indl&aelig;ser
            data...</span></td>
          <td height="30">
            <input type="text" name="progressbarPercent" value="0%" size="10" readonly>
          </td>
        </tr>
        <tr align="center">
          <td height="32" colspan="2">
            <table width="300" border="0" cellspacing="0" cellpadding="0" height="32">
              <tr>
              <!--- Insert 20 whitespaces --->
              <cfloop index="int_Counter" from="1" to="20" step="1">
                  <cfoutput><td width="15" height="32"><img src="frames/gfx/progressbar_white.jpg" name="Block#int_Counter#" width="15" height="32" alt="Progress Bar"></td></cfoutput>
              </cfloop>
              </tr>
            </table>
          </td>
        </tr>
        <tr>
          <td height="27"> &nbsp;
            <input type="text" name="progressbar" readonly class="progressbar" value="Påbegynder indsættelse af data">
          </td>
          <td height="27">
            <div align="center"><a href="#" onMouseUp="MM_swapImgRestore()" onMouseDown="MM_swapImage('Image1','','frames/gfx/progressbar_ok_down.jpg',1)"><img name="Image1" border="0" src="frames/gfx/progressbar_ok.jpg" width="62" height="15"></a></div>
          </td>
        </tr>
        <tr>
          <td height="25" colspan="2">&nbsp;</td>
        </tr>
      </table>
    <p>&nbsp;</p>
    </td>
  </tr>
</table>
</form>

Men det virker ikke .. hvordan får jeg JS til at opfatte insBlock som navnet på det img felt der skal updates?