VLC tends to play almost all the formats out there.
Windows Media player, (I use it to play everythuing...)
But for most things you need to download the .avi codec, which can *also* be obtained here:
(Its free, and just install the codec, not the player, no spam, or ads or adware are added)
There is no ".avi" codec. AVI=Audio Video Interleaved, or something of the nature. There are many codecs, (divx, xvid, mpeg4, h.264) that will take the .avi extension. DIVX may solve the problem, but it's not the end-all be-all avi codec by any stretch of the imagination. You're much safer finding a K-Lite Codec Pack, just google that and you'll find it; has every codec you'll ever need, up to 2005, at least.