ต้องการเขียนส่งค่า insert_id ยังบันทึกค่า id_brand เป็น 0 ละครับ

<a href="products_detail.php?id=<?=$rec['id_brand']?>">Products Detail</a>

<form action="" method="post" name="form_add" target="_parent" onSubmit="JavaScript:return fncSubmit();" enctype="multipart/form-data"> 
<ul class="showInColumn_add">
	<li><u>Add</u></li>
    <li><input name="txt_id_brand" type="hidden" size="50" value="<?=$_GET['id'];?>"/></li>//ตรงนี้ครับ
    <li>Title :<input name="txt_title" type="text" size="50" /></li>
    <li>download File :</li><br />
    <li><input name="fileDownload" type="file" size="37px" /><font color="#FF0000">*.pdf only</font></li>
    <li>images :</li><br />
    <li><input name="fileUpload" id="fileUpload" type="file" size="37px" /><font color="#FF0000">*.jpg only</font></li>
    <li><input name="save" type="submit" value="Save" /></li>
</ul>
<?
$date_today=date("Y-m-d");	
	if(isset($_POST['txt_title']))
		{
$sql="INSERT INTO `tb_products_detail`(id_brand,title,download_file,images,date_today) VALUES ('$_POST[txt_id_brand]','$_POST[txt_title]','".time()."_".$_FILES["fileDownload"]["name"]."','".time()."_".$_FILES["fileUpload"]["name"]."','$date_today')";

	$q=mysql_query($sql)or die (mysql_error());
	if($q){
			redirect('products_detail.php');
		}else{
			alert('Can\'t insert');
		}
	//echo $sql;
	}//if
?>
</form>
<? } ?>