Search the Internet and you may find what you want.
The science is imperfect but one thing you need to consider is you want to find a method to convert .bsp to 3DS or another format and then to .x
You may need multiple progs to achieve this. One that will open a .bsp file that can also output the result in another file format, that you might then convert any way you can to .x file. You may have to reset all textures following conversion from .bsp - then again maybe not.
As I am not a DBPro guy I have no idea if that could help. sorry.