Hello!
There is one workaround for this problem.
The TGA format is not supported by DirectX 10.
It is true, but is available on library GDI+.
You can load such file by using GDI+, then convert it
into GIF or other suitable graphics format (making it by GDI+ too).
The created resource you may save as a new file
or load it directly into DX via RAM.
Wlodek K.