With SWF Helper you can view thumbnails of Shockwave Flash files by Macromedia Inc.
Author: Alexander Mazuruk
Link: http://www.shuriksoft.com/opus/swfh.zip
Alternative Link: http://wisefm.com/swf-helper/
Note that this plugin is just for thumbnails of SWF files. You can already displays SWF files in the Viewer Pane using the ActiveX plugin which comes with Opus.
Also note that some the plugin may take a long time (several seconds) to identify some SWF files. If you're in a folder containing SWF files then having the plugin installed could make you wait longer for the file information columns, or thumbnails, to populate. (It only seems to affect some SWF, and you can always disable the plugin if you run into the problem a lot, so still give it a try if it sounds useful. I'm just mentioning it so people know how to fix the problem if they run into it.) --Leo
Update: Seems to crash Opus with some input files and the current (May 2009) version of Flash. --Leo