I keep several versions of blender on my computer because I use different plugin for various things.
I prefer this exporter its old and somewhat picky and can take a while to export.
http://xoomer.virgilio.it/glabro1/Be aware this exporter is very picky and it is best if your mesh is just one part.
I have problems if I try to use a mesh where the hair and shoes are a separate mesh.
Blender can be picky and new versions of Blender are coming out all the time. An exporter
can fail because of something as simple as an umlaut in the script.
As for exporting a .x file See this tutorial it will detail what script changes will need
to be made to a .x file.
http://www.wisdomspiral.com/tutorial_export_3d_into_game_engines.htmlIf the file exported fine but does not work in the game engine I often find one of the main causes is
that I have not done the weight painting correctly and have missed a part of the mesh.
I hope this helps you.