First of all, the files appear to be in TrueVision TGA (TGA version 2).
http://www.digitalpreservation.gov/...fdd000180.shtml
If you run a 'strings' tool against the tga files, you will see:
TRUEVISION-XFILE
For whatever reason, even the IrfanView viewer cannot view it:
http://www.irfanview.com/
So either IrfanView does not read TGA2 files, or the files are corrupted. I have to believe the latter.
In any case, you are starting with a BMP file you claim. Another TGA editor that I have used is DogWaffle. I have used successfully on Everquest TGA files.
http://www.thebest3d.com/dogwaffle/free/
There is a commercial and a freeware (v1.2) version.