In theory the bitmap should lay over the object using pix_texture, but that is not always the case in practice. I added the ability to select groups to allow different textures for different parts of the model. You need one model object per group to do this.
In part 4 you demonstrate uv mapping with a bitmap. Have you successfully got those uv mapped bitmaps onto geometry within gem? Do you just include the bmp in the same folder with the obj and mtl?