problem s IE a appendChild

<script>
function addEvent() {
    var pocet = document.fieldset.length-2;
    var max = 6;
      if (pocet <= max) {
      var tab = document.getElementById("table").insertRow(-1).insertCell(0);
      var new_input = document.createElement("input");
        new_input.setAttribute("id","picture"+pocet);
        new_input.setAttribute("type","file");
        new_input.setAttribute("name","picture"+pocet);
        tab.appendChild(new_input);
    }
 else alert("Je mozne uploadnut maxim\xE1lne " + max + " obrazkov");

}
</script>
<fieldset>
<legend>Pridaj inzerat - Krok 2 z 2</legend>
<form action="add.php" onsubmit="return verify_ad()" enctype="multipart/form-data" id="fieldset" name="fieldset" method="post">

<table width="100%" id="table" name=table>
<tr><td>Upload obrazku: povolene formaty: *jpg, *png, *gif<br />{$maxsize}</td></tr>
<tr><td><input type="file" name="picture1" id="picture1" /></td></tr>

</table>
<table>
<tr><td>
<input type="hidden" value="{$smarty.session.id}" name="id" id="id"  />
<input type="button" onclick="addEvent();" value="Pridaj upload" /> <input type="submit" value="Pokracuj" /></td></tr>
</table>
</form>

</fieldset>

var pocet = document.fieldset.length-2;