Well LW is designed using Java & requires Java to be installed in order to operate.

As for default program ... just go to any folder on your computer such as the desktop & choose a video file. Then go to File>properties ... etc. Setting Default video app (if that's the instruction link you're refering to.)
ie: your video files are stored on your hard disk drive so find the location of one of them. You can't set default within LW. But you can go to the LW Library window, select Saved Files & press the Explore button & this will open the folder up for you. Then you can set default. (I hope that made sense lol)