Yeah I think this was a weird bug that I came across once [Was not sure if it was the download version of Dark Matter I or the DVD version, I think I only use the download version now], there were I think .3ds? folder versions of models and .x models and one had .bmp textures and another had .dds textures but for each model folder the textures were in opposite folders.......
Strangely I only have .x models with .dds textures now...
Dark Matter II appears to mainly use .bmp
Before mention is made about them being laying on their back, this is something you need to fix yourself but there are code bits here and there on setting them up, but I have issues with this... need to look at it again... hopefully that book tells you how to load and reposition them properly, I might check that myself now
EDIT
Also, welcome to the forums!