klik.. load

<select name=pay class=pay>
    <option>Pilih tipe
    <option value=1>Umum
    <option value=2>Perusahaan
    <option value=3>Asuransi
</select>
<div id='payForm'>

</div>

<script>
$(".pay").change(function(){
    url='index2.php?showForm='+$(".pay").val()+"&r="+Math.random();
    $("#payForm").html('harap tunggu');
    $("#payForm").load(url);
});
</script>