formmail uses a number of special fields for particular purposes...
email is one of them, realname is another. realname is shown as the sender of the email (which is mostly what you want).
why not derive it from your firstname + lastname. see the how to guide on the main www.tectite.com site.
you can also tell formmail to exlcude the realname field with the mail_options value called "Exclude":
HTML Code:<input type="hidden" name="mail_options" value="Exclude=realname" />