how to convert mp4 to divx?
The good old ffmpeg gives you the power ;)

ffmpeg -i input.avi -c:v libxvid output.avi


You can obviously fine tweak the command line with bitrate, audio in mp3 and so on.

es:

ffmpeg -i input.avi -c:v libxvid -b:v 512k -c:a libmp3lame -qscale:a 4 output.avi


This is for a single bitrate use, where you use a constant bitrate for every frame.

Otherwise you could go for a 2 pass bitrate where the 1st pass is used only for determine where is the best for allocate more data...

But you can also convert in xvid/divx Mpeg 4 Layer 2 using a quality preset where you don't put directly the bitrate wanted but just ask for a minimum visual quality respected where you will be less concerned about the final file size (it will be discovered only at the end).

-qscale:v 3 instead of the -b:v 512k that i used above