You can always test the prog my splitting a small size movie (that you know works...by that I meant you can watch it prior to splitting) file into specific parts...like 3 equal sections.
Then, after the split...your splitted movie file will look something like this>>>> movie.avi.001, movie.avi.002, and movie.avi.003...
Then click on the "join" tab on the prog to go to the location of the splitted files and click "join"...
When you can do that, you've mastered the art of splitting / joining files B)