Asp 2 Dropdown Box Onchange

Hi
Can anybody show me how to do 2 dropdown boxes which the second box will change the value according to the first drop box selection?
I succesfully made the value change but the first drop box also changed to its initial value.

Thanks in advance
the attachment is my code..

post ur code pls........

This is part of the code ""
sqlManufac = "SELECT * from category order by category_id"
if ProdTypeID = 0 then
sqlSubCat = "SELECT * from sub_category order by sub_category_name"
else
sqlSubCat = "Select * from sub_category where ProductTypeID = " + prodTypeId + " order by sub_category_id"

end if

response.write(sqlSubCat)


sqlCat = "SELECT * from product_type order by producttypeid"
If cmd = "Add" Then
sql = "select * from Product where Product_id = 0"
Else
sql = "select * from Product where Product_id = " & productID
sql1 = "select * from Hardware_dimension where Product_id = " & productID
Set rsDim = objConn.Execute(sql1)
End If

' Get a Record Set
set rsSubcat = objConn.Execute(sqlSubCat)
Set rsCat = objConn.Execute(sqlCat)
set rsManufac = objConn.Execute(sqlManufac)
Set rs = objConn.Execute(sql)

if (isnull(mainCatDesc) or mainCatDesc = "" ) and cmd <> "Add" then
Do Until rsManufac.eof
If rs("category_id") = rsManufac("category_id") Then
mainCatDesc = rsManufac("category_name")
catDescription = rsManufac("category_desc")
End If
rsManufac.movenext
loop
rsManufac.movefirst
end if

if (isnull(mainProdDesc) or mainProdDesc = "" )and cmd <> "Add" then
Do Until rsCat.eof
If rs("producttypeid") = rsCat("producttypeid") Then
mainProdDesc = rsCat("producttypename")
prodDescription = rsCat("producttype_desc")
End If
rsCat.movenext
loop
rsCat.movefirst
end if

'mainProdDesc

If cmd = "Add" Then %>
<form name="form1" method="post" action="maintainHardware.asp" onSubmit="return hardwareValidate()" enctype="multipart/form-data">
<input type="hidden" name="cmd" value="add_save">
<% ElseIf cmd = "Edit" Then %>
<form name="form1" method="post" action="maintainHardware.asp" onSubmit="return hardwareValidate()" enctype="multipart/form-data">
<input type="hidden" name="cmd" value="edit_save">
<input type="hidden" name="productID" value=<%=productID%>>
<input type="hidden" name="imagePath" value='<%=rs("Product_Image")%>'>
<input type="hidden" name="pdfPath" value='<%=rs("Product_pdf")%>' ID="Hidden7">
<% ElseIf cmd = "Delete" Then %>
<form name="form1" method="post" action="maintainHardware.asp">
<input type="hidden" name="cmd" value="delete_save">
<input type="hidden" name="productID" value=<%=productID%>>
<input type="hidden" name="imagePath" value='<%=rs("Product_Image")%>'>
<% ElseIf cmd = "View" Then %>
<form name="form1" method="post" action="searchHardware.asp">
<input type="hidden" name="cmd" value="View">
<% End If %>

<p>&nbsp;</p>
<p>&nbsp;</p>
<p>&nbsp;</p>
<table class=content border="5" width="654" cellspacing="0" cellpadding="0" height="280" align="center">
<tr class=contentrow1 align="center">
<td colspan="9" height="22"><b><%=cmd %> Hardware Product</b></td>
</tr>
<tr class=contentrow2 >
<td colspan="9" height="260">

<table class=record width="100%" border="0" cellspacing="0" cellpadding="0" align="center">
<tr>
<td width="30" height="33">&nbsp;</td>
<td width="82" height="33" align="right"><div align="right"><font size="-1"><strong>Product Type</strong></font></div></td>
<td width="16" height="33" align="center"><font size="-1"><strong> :</strong></font></td>
<td valign="center" height="33" colspan="4">
<%

Select Case cmd
Case "Add" %>

<select name="prodtype" onchange="window.location='maintainHardware.asp?cmd=Add&cid=' + document.forms[0].prodtype.options[document.forms[0].prodtype.selectedIndex].value">

<% Do Until rsCat.eof
If rsCat("producttype_desc") = mainCatDesc Then %>
<option value=<%=Server.HTMLEncode(rsCat("producttypeid"))%> selected><%=rsCat("producttypename")%></option>
<% Else %>
<option value=<%=Server.HTMLEncode(rsCat("producttypeid"))%>><%=rsCat("producttypename")%></option>
<% End If
rsCat.movenext

loop

try this........
<% Do Until rsCat.eof
If rsCat("producttype_desc") = mainCatDesc Then %>
<option value=<%=Server.HTMLEncode(rsCat("producttypeid"))%> if rsCat("producttypeid")=cid then response.write "selected"><%=rsCat("producttypename")%></option>
<% Else %>
<option value=<%=Server.HTMLEncode(rsCat("producttypeid"))%>if rsCat("producttypeid")=cid then response.write "selected"><%=rsCat("producttypename")%></option>
<% End If
rsCat.movenext

loop