Open filefields in new window or modal or other

Expounding on some basics you can enjoy. I did this in my /mytheme/template.php
Even if you do not use any modals such as Colorbox, the examples might help you adapt the code to meet your needs. I "flowered" up the output a bit to demo that you can tune the stuff to appear as needed:

function YOUR_THEME_NAME_file_link($variables) {
  $file = $variables['file'];
  $icon_directory = $variables['icon_directory'];

  $url = file_create_url($file->uri);
  $icon = theme('file_icon', array('file' => $file, 'icon_directory' => $icon_directory));

  // Set options as per anchor format described at
  // http://microformats.org/wiki/file-format-examples
  $options = array(
    'attributes' => array(
      'type' => $file->filemime . '; length=' . $file->filesize,
    ),
  );

  // Use the description as the link text if available.
  if (empty($file->description)) {
    $link_text = $file->filename;
  }
  else {
    $link_text = $file->description;
    // $options['attributes']['title'] = check_plain($file->filename);
    $options['attributes']['title'] = check_plain($file->description . ' (' . $file->filemime . ')');
  }

  // open files of mime types from the array below in colorbox or a new window
// colorbox etc
  $new_window_mimetypes0 = array('application/javascript',
                                'text/plain',
                                'text/css'
                                );
  $new_window_mimetypes1 = array('image/gif',
                                'image/jpeg',
                                'image/png'
																																);
// end colorbox etc

  $new_window_mimetypes2 = array('application/json',
                                'application/pdf',
                                'application/vnd.lotus-wordpro',
                                'application/x-msaccess',
                                'application/mp4',
                                'application/rss+xml',
                                'application/rtf',
                                'application/vnd.google-earth.kml+xml',
                                'application/vnd.google-earth.kmz',
                                'application/vnd.rn-realmedia',
                                'application/vnd.solent.sdkm+xml',
                                'application/vnd.wordperfect',
                                'application/wsdl+xml',
                                'application/x-font-ttf',
                                'application/x-7z-compressed',
                                'audio/x-pn-realaudio',
                                'application/x-tar',
                                'application/x-rar-compressed',
                                'application/x-shockwave-flash',
                                'application/xslt+xml',
                                'application/xspf+xml',
                                'application/x-stuffit',
                                'application/x-stuffitx',
                                'application/xhtml+xml',
                                'application/xml',
                                'application/zip',
                                'audio/basic',
                                'audio/midi',
                                'audio/mp4',
                                'audio/ogg',
                                'audio/webm',
                                'audio/x-mpegurl',
                                'audio/x-ms-wma',
                                'image/svg+xml',
                                'image/tiff',
                                'image/vnd.adobe.photoshop',
                                'image/x-icon',
                                'text/calendar',
                                'text/html',
                                'text/csv',
                                'text/sgml',
                                'video/x-flv',
                                'video/3gpp',
                                'video/mp4',
                                'video/mpeg',
                                'video/ogg',
                                'video/quicktime',
                                'text/vnd.wap.wml',
                                'text/vnd.wap.wmlscript',
                                'video/webm',
                                'video/x-m4v',
                                'video/x-msvideo',
                                'video/x-ms-asf',
                                'video/x-ms-wm',
                                'video/x-ms-wmv',
                                'video/x-sgi-movie',
                                'application/msword',
                                'application/vnd.visio',
                                'application/x-mspublisher',
                                'application/vnd.ms-powerpoint',
                                'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
                                'application/vnd.openxmlformats-officedocument.wordprocessingml.template',
                                'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
                                'application/vnd.ms-excel',
                                'application/x-msdownload');

  if (in_array($file->filemime, $new_window_mimetypes0)) {
    $options['attributes']['class'] = 'colorbox-800';
    $options['attributes']['rel'] = 'geshi-filter';
    // return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) . '</span>';
    return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) . ' [Modal Colorbox] (' . $file->filemime . ')' . '</span>';
  }

   if (in_array($file->filemime, $new_window_mimetypes1)) {
    $options['attributes']['class'] = 'colorbox';
    $options['attributes']['rel'] = 'nofollow';
    // return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) . '</span>';
    return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) . ' [Modal Colorbox] (' . $file->filemime . ')' . '</span>';
  }

  else if (in_array($file->filemime, $new_window_mimetypes2)) {
    $options['attributes']['target'] = '_blank';
  return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) .  ' (' . $file->filemime . ')' . '</span>';
  }
}

And jQuery function for the colorbox-800 class (resides in mytheme.js or whatever method you use for custom javascript functions).

(function($) {
$(document).ready(function()  {
        $(".colorbox-800").colorbox({
            iframe:true,
            fastIframe:false,
            innerWidth:'100%',
            innerHeight:'100%',
            transition:"elastic",
            opacity:.7,
            onComplete:function(){
              $.fn.colorbox.resize({width:'90%', height:'90%'});
            },
           });
          });
})(jQuery);

*note the class "colorbox" is Native to Colorbox and functions as long as "Colorbox" is installed.