To preview a file there must be a certain % already downlded. It will ONLY preview the amount that's downlded. eg: a full movie of 2 hours which is 700 MB in size. If you have downloaded 2% then you could only preview 2 mins of that movie. If you haven't downlded any of that movie then you can't preview it. Instead of preview, try launch instead with a movie you already have in your shared folders (if you have any.)

No program works within LW. What happens is that when you launch or preview a file LW will open the appropriate default player. eg: music & your default player is iTunes. Then when you launch or preview an mp3 then iTunes will open & play it. Likewise for video. Say you launch an mpeg movie then VLC (if it's the default) will open & play that movie.

You don't use LW to make a default video player b/c LW's media player cannot play video files. It can only play music. But because it's sometimes unreliable people often disable it thru options so their default audio player plays instead. For video it's always your default video player that will open everytime you preview or launch a movie file.