Help pulling variables from theme_render_template()

Hello,

I am trying to customize the output of the guestbook module. This is what I have in my template.php file:

function phptemplate_guestbook_entry($uid, $entry, $comment_entry = NULL, $zebra, $confirm_delete = false) {
$guestbook_variables = array('uid' => $uid, 'entry' => $entry, 'comment_entry' => $comment_entry, 'zebra' => $zebra, 'confirm_delete' => $confirm_delete);
return theme_render_template('/sites/all/themes/CYW/guestbook_entry.tpl.php',$guestbook_variables);
}

And I have a guestbook_entry.tpl.php file that is currently empty as I don't know who to display the variables.

If I try print_r($guestbook_array) I get nothing.

Any help appreciated. Thanks.