Help Needed - Quicktime & Codecs

I tried the apple forum - no success.
Anyways -- I have avi. files I want to make into mp4 so I can put them
on my ipod. I downloaded a converter to convert into mp4 - I try to play the
file in quicktime - the audio plays but the video doesn't. I tried downloading
almost all the codecs on the quicktime page - didn't work. I have the DVix
player it works with my wmp. - so I downloaded another DVix codec and put
it in quicktime folder. it still doesn't work. what am I doing wrong or am I not
doing?:ermm:

Thanks!