There is some confusion on this. DivX is a video compression codec, widely used for ditributing movies and TV shows over the internet. But DivX was also the name of a short-lived and rarely used technology for DVD video discs that was supposed to replace video-rentals. The idea was that you would pay a rental fee for the disc, but it would only be able to be played a few times before it would lock the user out. It was an interesting idea, but it was unpopular and failed before it even got off the ground.
If the format you are thinking of is the DivX codec, then you can download this from version-tracker as a quick-time plug-in. It seems to work 90% of the time, the other 10% of the time you might need to run some repair programs to fix up the file.
If you search for DivX on this forum you'll find plenty of threads about making and playing DivX video on the mac.