'Playing AVI files
In Windows it is rather easy to play an AVI file IF you have the correct codec installed. There is a whole lot of Windows applications available that can play AVI files. The most widely used being Microsofts own Windows Media Player available through their website. If you do not have the codec needed to play the file Windows Media Player will not be able to play it (It might be able to play the audio stream within the file while no images will be showed).'
what is the right codec for avi files in wmp 
where can i get one?
AVI is just a container. You need to figure out what codec was used to create that movie stream with something like GSpot, and then install the appropriate codec.
i need avicodec
try this codec
http://www.free-codecs.com/Avid_AVI_Codec_download.htm