how to change sender in contact.php

I would like to change contact.php so that the email I receive has the form's sender's email as being sender of the message and not the site's email address. Sometimes email from the form is lost since we think it's email from us that we've Cc'd our site email on. I hope this makes sense; it's late :)

I think this is the area of contact.php that needs tweaking but I can't seem to get it to work properly:

$sSenderName = process_db_input( $_POST['name'] );
$sSenderEmail = process_db_input( $_POST['email'] );
$sLetterSubject = process_db_input( $_POST['subject'] );
$sLetterBody = process_db_input( $_POST['body'] );

$sLetterBody = $sLetterBody . "\r\n" . '============' . "\r\n" . _t('_from') . ' ' . $sSenderName . "\r\n" . 'with email ' . $sSenderEmail;

if( sendMail( $site['email'], $sLetterSubject, $sLetterBody ) )
{
$sActionText = _t_action('_ADM_PROFILE_SEND_MSG');
}
else
{
$sActionText = _t_err( '_Email sent failed' );
}
}