In order to play movies you must have whats called a codex. Basically think of it like this. If you take a .txt it can open up with programs that can read the txt file code. You wouldnt wanna try opening a txt with photoshop. Same goes with movies. Only its a little harder to determain the "decoder" for it. Something I would recommend getting is a program called avicodex.
http://avicodec.duby.info/ This program will tell you what the foles audio and video codex were used to make the file and suggest where to get the programs to play it. This program is designed for the pc but might give ya a better idea on how to open the avi file. Another great site with FAQ and programs to encode/decode video is
http://www.dvdrhelp.com/ or formally known as vcdhelp.com You will find alot of useful info on playing and making your own movies as well. If ya have any more questions feel free to contact me.