I already installed a codec, but nothing happened ! why ?

I installed a codec, called codec 5.0 (it's from www.codecs.com). I already installed it, and saved it in my doents, but nothing happened when i tried to play my .avi format video in the WMP ! what went wrong ? was it where I saved it ? by the way, i'm not computer adminstrator, I'm a limited account on windows (if it has anything to do with it).