I've looked everywhere but cannot find any info on adding an "Attach File" field to our contact us form. I'm looking in the following files, but I just don't have the know-how to get the coding right.

includes/languages/english/contact_us.php
I've added define('ENTRY_ATTACH','Attach File:');

includes/modules/pages/contact_us/header_php.php
I've done nothing to this yet.

includes/templates/template_default/templates/tpl_contact_us_default.php
I've done nothing with this yet.

Help?

Much appreciated,
Lisa