Open the film in Film viewer, get to the scene youd like a screenie from, hit "pause", adjust view/angle, click on "Full Screen" button to the right. Wait till all the graphics are loaded again, then "Print Screen" on your keyboard. Open Photoshop (or any other pic editing software - even paint works). Paste the screenie in a new file.
If you want to have really good looking eye candy, backup your video.cfg. then Go ingame and change vid settings to full eye candy. (Maybe even highres textures). Swich on anti aliasing in your desktop properties. Then open film in viewer and take screenies as described above.
For further screenshots rename the new video.cfg and keep it, repaste your backup in. The only thing youll have to do each time then is replace the vid-cfg file and let AH rebuild the cache folder.