@rms
Hi, I made an Arexx script for this:
http://home.swipnet.se/~w-160129/progs/video-cut.rexx

Go to "Ambient Settings", select "MIME", double click on "video", click "Add" and configure like this:
http://home.swipnet.se/~w-160129/progs/video-cut.png

Don't forget to change last line in video-cut.rexx to your Mencoder path.

Now you can right click on any video and run the script, type in start position and length of the video clip.

Use MPlayer for visualisation as jPV said.
This is not a GUI program but still very handy.