I saw a question from PapaXpress on the 3DC forum at Amabilis that asked: "What is happening is whenever I use a TGA for a texture the component turns translucent. I can see the all my edits to the file, but its all "see through", if I switch back to a BMP, its opaque again."
I found the answer to that myself some time ago:
When you use the material, in the Advanced Options, Primary Tex. Alpha Ch., instead of Standard, set it to Ignore. That way, it won’t be transparent, although if you’ve also used bump mapping, it might appear silvery.
Incidentally, the Advanced Options can’t be seen (or modified) in the Material Manager, so you have to set the ignore when you apply the material directly