Contact form with mailer.php "From" header

Hi,
I’m an extreme noob at php but used the mailer.php script from this site to add a contact form to my web site. It works fine, except that when form is submitted, in every email I receive, the “From” header reads “anonymous@neptune.catalog.com”. (Web host is WebHero.) The sender’s email address does appear in the body of the email, but is there a way to make the sender’s email address appear in the “From” header of the email? Or is it supposed to work this way?

Sorry for such a dumb question!

Susan