Here is a very specific command that I'll post publicly, as someday one other person just may search for it:
The following loads in a MythTV NUV file containing a letterboxed, telecined film (...or Battlestar Galactica episodes). The video was captured at 528x480, 29.970fps. It crops the borders, detelecines to 23.976fps, and scales in the X-dimension to 480x360. This 4:3 aspect ratio makes it possible to play fullscreened on my Philips DVP642/17, which will get stretched back to the original 16:9 by the widescreen TV. The codec is lavc's msmpeg2, which seems to be the only one that works with the Philips player. Since the NUV is from digital cable, I just pass the AC3 audio through. You could also mp3lame it.mencoder -vf crop=528:360:0:60,pullup,softskip,scale=480:360 -ovc lavc -lavcopts vcodec=msmpeg4:vbitrate=1200 -oac copy -ofps 24000/1001 input.nuv -o output.avi
Add two-pass options if you like.
*whew* trial and error on mysterious hardware sure is fun. If only there was some kind of universal computing machine I could use to output video directly to the big TV.