Okay, I worked through this problem yesterday with Sam's direct help, so thought it might be worthwhile posting here for future reference...

Required: the ability to attach a downloadable document to a page, and to give it a 'friendly' name for displaying.

So, step 1, set up the Page class...

<?

class Page extends SiteTree {
   static $db = array(
      "FileTitle" => "Text"
   );
   static $has_one = array(
      "Download" => "File",
   );
   static $defaults = array(
   );

   function getCMSFields() {
      $fields = parent::getCMSFields();
      $fields->addFieldToTab("Root.Content.Download", new TextField("FileTitle"));
      $fields->addFieldToTab("Root.Content.Download", new FileIFrameField("Download"));
      return $fields;
   }

}

class Page_Controller extends ContentController {

}

?>

...then, on the page.ss template...

<% if FileTitle %>
<a href="$Download.URL">$FileTitle</a>
<% end_if %>