I don't know about FRAPS, but if you use <alt> R and open the film in AH Film Viewer, just go to the spot you want a screenie from, set up the angle you want, then click "View Fullscreen" on the right. Press Print Screen on your keyboard (located above the insert, delete, home keys), and open up Paints and edit paste. Now just save it.
NOTE: Move your mouse out of the screen when in Full screen view so you don't get your mouse in the picture too.