Mythran@ you don't need to have an alpha channel as a third skin with 24 bits/pixels file! Please check you messages!
Everything works pretty nice (MED viewer):
There is another small alpha problem, but I always face it myself as well, you can fix it by using the material, that was suggested by Ch40zzC0d3r!
First:
Second:
Maybe there are some other ideas, how to fix this, I would be glad to hear them too.