If DivX does not open in Vegas though DivX is installed in most cases either only a DirectX version instead of a VfW version is installed, or XviD was installed later or/and something is going wrong with the DivX FourCC and a FourCC changer should help.
DivX works fine for me on several systems both for export and import. What I've never tested is 2-pass DivX encoding. No glue if this works.