if you name the text fields like this:
<input type=text name="email[1]">
<input type=text name="email[2]">
then they will automattically be put into an array ($email), and you can run the array through array_unique() like this:
$email = array_unique($email);
this will return an array with only unique email addresses.
if you can't get them into an array automatically by changing the text field names, you can manually put them into an array. This is only one way of doing it too, using manual string comparisons would also work, and I'm sure there are even more ways.
Find more info at http://www.php.net/manual/en/function.array-unique.php
