not sure but it could be....
this is assuming you got the divx codec installed
the 'explorer sucking 99% cpu' thing could be because it's busy scanning the .AVI file.. which usually means it's lacking the avi index... that is.. broken AVI file... (not unusal when getting from the net)...
with this, mediaplayer (either version) can't play it...
easy fix is to download a little program called DIVFIX.. can't remember where i got it but im sure it's not hard to find from a good searchengine.
it scans the avi file and makes a new index for it... which usally makes it fully playable...
worth a try....