You have to be playing the Divx file with mplayer2 in order for the change to stay. changing it in "decoders configeration" in START, programs, divx doesn't help mush.
Here's what you do:
Go to "start" then "Run"
Now,, input "mplayer2" without the" " then [enter]
The old media player should open, now open any divx file
when the file is playing , right click on the screen then select "properties" then "Advanced" now select "divx decoder filter"
Now move the slider to the max, click "apply"
Your setting will now stay.
But Even with the setting at Max it doesn't improve a whole lot. it will only help smooth out the high compress qualitys a little bit. For the new nicely encoded divx, you wouldn't even notice it much.
I like ffdshow's post processing more, because there's a auto setting, and it use around 50% less cpu power than the normal divx decoders.