test.html

<script src="jquery.js"></script>
<script type="text/javascript">
	// 2006-08-21 - Created
// 2006-11-05 - Modified - head and body
function addColumn(tblId)
{
	var tblHeadObj = document.getElementById(tblId).tHead;
	for (var h=0; h<tblHeadObj.rows.length; h++) {
		var newTH = document.createElement('th');
		tblHeadObj.rows[h].appendChild(newTH);
		newTH.innerHTML = 'KW2' + h + ', cell: ' + (tblHeadObj.rows[h].cells.length - 1)
	}

	var tblBodyObj = document.getElementById(tblId).tBodies[0];
	for (var i=0; i<tblBodyObj.rows.length; i++) {
		var newCell = tblBodyObj.rows[i].insertCell(-1);
		newCell.innerHTML = '[td] row:' + i + ', cell: ' + (tblBodyObj.rows[i].cells.length - 1)
	}
}
function deleteColumn(tblId)
{
	var allRows = document.getElementById(tblId).rows;
	for (var i=0; i<allRows.length; i++) {
		if (allRows[i].cells.length > 1) {
			allRows[i].deleteCell(-1);
		}
	}
}
</script>

<form>
<select onchange="addColumn('tblSample')">
	<option value="1">1pcs</option>
	<option value="2">2pcs</option>
	<option value="3">3pcs</option>
</select>
</form>

<table border="1" id="tblSample">
	<thead>
		<tr>
			<td>Error</td>
			<td>KW2</td>
			<td>KW3</td>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td>Error 1</td>
			<td><input type="text" name="error[]"></td>
			<td><input type="text" name="error[]"></td>
		</tr>
		<tr>
			<td>Error 2</td>
			<td><input type="text" name="error[]"></td>
			<td><input type="text" name="error[]"></td>
		</tr>
		<tr>
			<td>Error 2</td>
			<td><input type="text" name="error[]"></td>
			<td><input type="text" name="error[]"></td>
		</tr>	
	</tbody>
</table>