Z-Sorting...
Your Skin contains an Alphamap, so the Model seems to be Transparent.
Have a look into the GS Wiki (you'll find the Wiki link here in the upper left Corner).
Search for Alpha Test Material, download this and assign the Acion to Your Model.
Or the Other Way, go into MED -> Skin Settings and deselect the 32Bit Texture Flag.
Now the Model must be look okay.
Regards Sebastian
Tutorials:
[Blender]Terrain creation ENG/GER
[Blender]Low Poly Tree Modeling
[GIMP]Create a Texture for Terrains
CLICK HERE