2 noob questions!

1. Can PS3 play AVI files?

2. Is there a way to make downloaded videos from the PS Store in preview mode? 

1. i don't think so

2. nope

1.) You can no stream avi movies to yor PS3 since the 1.8 update.  I dont know all the details but I do know that Nero makes a media center that can do it, not sure how, but I have seen threads on other forums, I have yet to try, but have seen video proof.

2.) Are you talking about a small video preview of each video you downloaded? If so, start the video, then press triangle. This will pop a menu up, then selct change icon. This will then take the next 15 secs of video and make it the icon. If this is not what you are talking about, then I have no idea what your asking, lol.

for avi files

you can also put YDL on your PS3 from there go onto the net and download VLC player.