duffer,
You can either make a program that follows the x file requirements or code your own format.
the x file can be expressed as a text file or binary file.
when you are writing out the data u follow the format of the file by making up a text file to export out the required mesh data /centerpoint / texture / normal data and animation data.
If u take a cube in any package that exports to x, export it thusly then open that file in notepad u will see the format.
You may want to track down on the web a file format reference for x files
I think it used to be called d3d and Im not sure if this info will help
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directx9_c/directx/graphics/reference/d3d/enums/d3dformat.asp
this is prolly more closer to home
http://astronomy.swin.edu.au/~pbourke/geomformats/directx/
Theres no stopping you writing your own x file exporter in ascii or binary if your really clever but its easier to bugtest in ascii.
If u think thats definately for the hard basket then just be patient and keep studying the commands until something is created that performs this.
If nothing is created that will do this then request for methods to solve it
