insert into your_table
(surname, firstname, emailaddress)
select distinct '#form.surname#', '#form.firstname#',
'#form.emailaddress#'
from some_small_table
where not exists
(select surname
from yourtable
where surname = '#form.surname#'
and firstname = '#form.firstname#' )
By the way, how are you going to cope with two people having
the same name?