Guess what? I got it working! smile
I have to save the blend file with the second skin, before I export it.

Nonetheless, a further question:
- Does it need a special material setting to see the combination of the skins ingame? At least, the preview in MED doesn't show both at once.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt