You will need
The DivX codec installed in your system and a plugin for it in your browser. Make sure your browser has it.
MediaStream plugin installed in your ruTorrent.
FileManager plugin installed in your ruTorrent.
If you don't have them on your seedbox, here are the commands to download both:
To configure MediaStream, create a folder on your document root for the viewer.php file, create a symbolic link to it and set permissions to your web server:
cd /<your http server document root>/rutorrent/plugins/
sudo svn co http://svn.rutorrent.org/svn/filemanager/trunk/mediastream
sudo svn co http://svn.rutorrent.org/svn/filemanager/trunk/filemanager
Edit ../rutorrent/plugins/mediastream/conf.php and configure the url to point to the view.php link you just created:
sudo mkdir -p /<your http server document root>/stream/
sudo ln -s /<your http server document root>/rutorrent/plugins/mediastream/view.php /<your http server document root>/stream/view.php
sudo chown www-data: /<your http server document root>/stream
sudo chown www-data: /<your http server document root>/stream/view.php
And refresh your ruTorrent (CTRL+F5)
$streampath = 'http://<your hostname or IP address>/stream/view.php'
When you have it all done it's simple
Go to the File Manager and navigate until you find a video file
Right click it and select View
A video plugin window will open, wait it to buffer your video