By xdiv, do you mean Xvid?
http://sourceforge.net/projects/ffdshow
ffdshow is DirectShow and VFW codec for decoding/encoding many video and audio formats, including DivX and XviD movies using libavcodec, xvid and other opensourced libraries with a rich set of postprocessing filters.
If you can not import Xvid into WMM, then you might need to first transcode it to a different avi container format.
You can do this with Nandub. Actually you can do quite a bit with nandub, which might make WMM unnecessary.
http://www.divx-digest.com/software/nandub.html