You don't know what type of DivX movie it exactly is, do you?
How are your "Preferences" settings on tabs [DivX;-) 3.11] resp. [DivX], with respect to "CPU quality" resp. "Postprocessing level"? (Set both sliders to the far right).
(You might also wish to experiment with "film effect").
Alternatively you could also directly alter settings of the decoder codec/filter, by right-clicking on the movie window and then select "Properties" and subsequently the video decoder.
PS: Yet another setting you could possibly change is setting on the [General]-tab of "Preferences" i.e. "Process priority" (at bottom-left)