You can probably tackle this problem in different ways. If you did not install any codecpacks
(I strongly advise against using whole codec-packs. One is tempted to install as much as possible, which only leads to conflict-situations and problems!) and installed DivX5.1.1., have a look at its settings on Tab "Quality". (You can reach filters/codecs through BSPlayer's "Options"/"Filters" (with a movie loaded)). However, for DivX5.1.1 codec its settings can also be reached
directly through [Start] "Programs"/"DivX"/"DivX codec"/"Decoder configuration Utility".
If "Support Generic Mpeg-4" is checked (selected) my XViD movies play using (i.a.) DivX-decoder. If this box is unchecked, same movies will use XViD's codec and XViD codec will be shown under "Options"/"Filters", where you also can set its properties.