select.htm
<script>
function openWin(a) {
window.location="xz.asp?a=" + a;
}
</script>
<form id="form1" name="form1" method="post" action="">
<select name="a" onchange="openWin(this.value)">
<option selected="selected"></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</form>
xz.asp
<%
Dim act
act=request.QueryString("a")
%>
<form id="form1" name="form1" method="post" action="<%=act%>.asp">
<input type="submit" name="Submit" value="确定" />
</form>