if you want to fill it in the fields from a database then the best you can do is do a js onchange (on the dropdown) to post the form to a new window which contains the asp to interface with the db. using opener.focus at the very head of the page (in js tags) means that it shouldn't be too annoying for users. then create a bunch of hidden fields in the second page like so:
<form name="theform">
<input type="hidden" name="thefield" value=<%=vrec("thefield")%>>
<input type="hidden" name="thefield2" value=<%=vrec("thefield2")%>>
</form>
Then run some js like this:
<script language="javascript">
opener.document.form.field1.value = document.theform.thefield1.value
opener.document.form.field2.value = document.theform.thefield2.value
</script>
Downside of this is it doesnt work if people have blocked popups, or if they've disabled js, and it is a bit messy.