ต้องการเลือก Dropdownlist อำเภอ แล้วให้รหัสไปรษณีย์ออกที่ textbox ครับ

<script language = "JavaScript">
//**** List Province (Start) ***//
function ListAmphur(SelectValue)
{
frmMain.ddlAmphur.length = 0
frmMain.ddlDistrict.length = 0
//*** Insert null Default Value ***//
var myOption = new Option('','') 
frmMain.ddlAmphur.options[frmMain.ddlAmphur.length]= myOption
<?
$intRows = 0;
$strSQL = "SELECT * FROM amphur ORDER BY AMPHUR_NAME ";
$objQuery = mssql_query($strSQL) or die ("Error Query [".$strSQL."]");
$intRows = 0;
while($objResult = mssql_fetch_array($objQuery))
{
$intRows++;
?>          
x = <?=$intRows;?>;
mySubList = new Array();
strGroup = <?=$objResult["PROVINCE_ID"];?>;
strValue = "<?=$objResult["AMPHUR_ID"];?>";
strItem = "<?=$objResult["AMPHUR_NAME"];?>";
mySubList[x,0] = strItem;
mySubList[x,1] = strGroup;
mySubList[x,2] = strValue;
if (mySubList[x,1] == SelectValue){
var myOption = new Option(mySubList[x,0], mySubList[x,2]) 
frmMain.ddlAmphur.options[frmMain.ddlAmphur.length]= myOption                  
}
<?
}
?>                                                                  
}
//**** List Province (End) ***//
//**** List Amphur (Start) ***//
function ListDistrict(SelectValue)
{
frmMain.ddlDistrict.length = 0
//*** Insert null Default Value ***//
var myOption = new Option('','') 
frmMain.ddlDistrict.options[frmMain.ddlDistrict.length]= myOption
<?
$intRows = 0;
$strSQL = "SELECT * FROM district ORDER BY DISTRICT_NAME ";
$objQuery = mssql_query($strSQL) or die ("Error Query [".$strSQL."]");
$intRows = 0;
while($objResult = mssql_fetch_array($objQuery))
{
$intRows++;
?>
x = <?=$intRows;?>;
mySubList = new Array();
strGroup = <?=$objResult["AMPHUR_ID"];?>;
strValue = "<?=$objResult["DISTRICT_ID"];?>";
strItem = "<?=$objResult["DISTRICT_NAME"];?>";
mySubList[x,0] = strItem;
mySubList[x,1] = strGroup;
mySubList[x,2] = strValue;
if (mySubList[x,1] == SelectValue){
var myOption = new Option(mySubList[x,0], mySubList[x,2]) 
frmMain.ddlDistrict.options[frmMain.ddlDistrict.length]= myOption                  
}
<?
}
?>                                                                  
}
//**** List Amphur (End) ***//
</script>

จังหวัด
<select id="ddlProvince" name="select_province" onChange = "ListAmphur(this.value)">
<option selected value="">---เลือก---</option>
<?
$strSQL = "SELECT * FROM province ORDER BY PROVINCE_NAME ";
$objQuery = mssql_query($strSQL) or die ("Error Query [".$strSQL."]");
while($objResult = mssql_fetch_array($objQuery))
{
?>
<option value="<?=$objResult["PROVINCE_ID"];?>"><?=$objResult["PROVINCE_NAME"];?></option>
<?
}
?>
</select>

อำเภอ
<select id="ddlAmphur" name="select_amphur" style="width:120px" onChange = "ListDistrict(this.value)"></select>

ตำบล
<select id="ddlDistrict" name="select_district" style="width:200px"></select>

รหัสไปรษณีย์
<input type="text" name="ZIPCODE" >