Viewing AVI files

I’m having problems viewing certain .avi files with Microsoft Media Player (MMP) and Windows Media Player (WMP). I have a 64MB AGP Video card which I think is more than enough, and for some reason evertime I load it up with MMP, it’ll only play thesound of the video, when I open it with WMP I get an error “Unable to download an appropriate decompressor” I checked support, and does not give me a definite answer. I know the video works on other systems. Any help is appreciative