The solution/hack involved a customization to the Upload module, replacing the theme_upload_attachments() function with the customized version below. The idea was to have the content manager add a prefix to the filenames that would identify the category, and the software would take care of the rest.

Some notes:

• [+] It can’t get much easier than adding a prefix to a file before you upload it to the web site.
• [+] FTP file listings are now sorted by category in the Drupal files/uploads folder.
• [-] If the content manager makes a mistake in naming a file, she has to remove the upload, rename the file on her file system, and re-upload.

Here’s the modified function for Drupal 4.7, use at your own risk. At some time before we launch the site I’ll upgrade to Drupal 5.1, and post a modified version of the function for 5.1.

/**
* Displays file attachments in table
*/
function theme_upload_attachments($files) {
  $header = array(t('Name'), t('Size'));
  $spec_rows = array();
  $dsgn_rows = array();
  $inst_rows = array();
  $case_rows = array();
  $rows = array();
  $str = array();

  foreach ($files as $file) {
    if ($file->list) {
      $href = $file->fid ? file_create_url($file->filepath) : url(file_create_filename($file->filename, file_create_path()));
      $text = $file->description ? $file->description : $file->filename;

      if (strpos($file->filepath,'spec_') != false) {
        $spec_rows[] = array(l($text, $href), format_size($file->filesize));
      } elseif (strpos($file->filepath,'dsgn_') != false) {
        $dsgn_rows[] = array(l($text, $href), format_size($file->filesize));
      } elseif (strpos($file->filepath,'inst_') != false) {
        $inst_rows[] = array(l($text, $href), format_size($file->filesize));
      } elseif (strpos($file->filepath,'case_') != false) {
        $case_rows[] = array(l($text, $href), format_size($file->filesize));
      } else {
        $rows[] = array(l($text, $href), format_size($file->filesize));
      }
    }
  }

  if (count($spec_rows)) {
    $str[] = '<h2>Product Specifications</h2>';
    $str[] = theme('table', $header, $spec_rows, array('id' => 'attachments'));
  }
  if (count($dsgn_rows)) {
    $str[] = '<h2>Design Information</h2>';
    $str[] = theme('table', $header, $dsgn_rows, array('id' => 'attachments'));
  }
  if (count($inst_rows)) {
    $str[] = '<h2>Installation Guides</h2>';
    $str[] = theme('table', $header, $inst_rows, array('id' => 'attachments'));
  }
  if (count($case_rows)) {
    $str[] = '<h2>Case Studies</h2>';
    $str[] = theme('table', $header, $case_rows, array('id' => 'attachments'));
  }
  if (count($rows)) {
    $str[] = '<h2>Other Downloads</h2>';
    $str[] = theme('table', $header, $rows, array('id' => 'attachments'));
  }
  return implode('',$str);
}