Is "Support Generic Mpeg-4" of the DivX-decoder
deselected?
What version of XviD are you using?
P.S.: I don't use this version any more; the pre 1.xx-version which I still have installed (and can experiment with) is version 0.86 build 501 of 16 Sep. 2003.
This is a link to my
Help-to-Help post for version 0.86