You will need cutlisteditor and moviecut from the extensions plugins...
Once installed, highlight the movie you want to cut, and then press the menu button. There's an option in there to use the cutlisteditor. Go to the position where the movie starts, pause it, and then press the "OK" button. Then, select the "Remove before this position" or something like that. Then, go to the end position of the film, and pause again. Press the OK button, and choose the "Remove after this position". This will leave you with the movie left. Then, exit the cutlisteditor, choose the "Cut movie" or "Movie cut" (can't remember exact name). This will give you some options. I'd choose the "Cut this movie to a new file" or something along those lines. You can then check that it worked properly before deleting the cut, in case you didn't do it properly