WMV = asf a container from Microsoft. MPEG-4 is a set of specifications defining audio, video, subtitles, container, systems (interactivity), etc. Since WMV is a container I guess you would be comparing it to MPEG-4 Part 14 which is the container, mp4. You could also compare WMV9 aka VC-1 which is MS' current video codec. The comparable MPEG-4 standard would be Part 10 aka AVC aka H.264, although VC-1 does share a lot with it. Then you also have WMA vs. aac in the audio department. You really need to be more specific about what you want to know. Otherwise you could try looking up the specs or some wiki articles on the different containers/audio/visual formats.
