The script is no importer, just an exporter.

It works perfectly for me, using currently newest Blender version 2.45. Are you sure you have put the "export_3dgs_mdl7.py" into the right folder?

...\Blender Foundation\Blender\.blender\scripts

If so, maybe you simply overlook the entry in the export menu. It should appear at nearly the top. It says 3D gamestudio MDL7 (mdl)