DivX Validator is an old tool that is pretty much useless, it gives the wrong type to some versions of DivX (there are like four different ones used right now).

DivX Doctor does other things to the file, appart from fixing filetypes to let quicktime play the files correctly, like changing them from .avi to .mov for instance.

But the best tip for people using OS X and wishing to view DivX files, even on pretty low end macs, is to use VLC (VideoLAN Client), a program ported from Linux that playes all matter of video formats, or MPlayer, another Linux-port. Both are good, but VLC has been better for me (only problem is some videocards, like mine, won't give a picture from VLC if you don't switcch to thousands of colours first. But it's no big deal since most DivX files aren't of stunning quality anyway). MPlayer's GUI for OS X isn't very good either, so you'll most likely have to use the terminal to use it, which might deter alot of users i guess.