If you can't see objects produced by Conv3ds.exe after loading them into the Direct3DRM viewer, use the scale option -s with a scale factor of approximately 100. This will increase scale of the objects in the X file.
If, after loading the object into the viewer and switching from flat shading into gourard shading the object turns dark grey, try converting with the -N option.
If the textures aren't loaded after the object is converted, ensure that the object is referencing either .ppm or .bmp files by using the -e option. Also ensure that the textures' widths and heights are a power of 2. Make sure the textures are stored in one of the directories in your D3DPATH.
Currently, Conv3ds.exe can't handle dummy frames used in 3DS animations. It ignores them. However, it will convert any child objects.