i do not know how this can be done in front page, but i am providing a simple script which you can add to your pages to do this for you.
enter the following script onto the results page the page that comes after the form
********************************
<%
Dim mail1, mail2, mail3
mail1=request.form("first email field name"

mail2=request.form("second email field name"

if mail1=mail2 then
%>
(place here the full page, that displays the results.. ie all your current script)
<% else
response.redirect("address of the form page?mail3=error"

end if %>
*********************************************
place the following code, at the top of the form page
****************************************
<%
dim mail3
mail3=request.form("mail3"

if mail3="error" then
Response.write ("you have not put the same email address in both forms"

end if %>
**********************************************
that should solve the problem,
hope it helps
thjanks