TreeMagik G3 supports TGA's. But the program is buggy as all hell, and I've found that to keep it from crashing, all the image types in, say, the leafskins directory (or any of the skins directories) have to be the exact same type--if you mix a .bmp in with the tga's for example, the program will crash when you go to select a skin.

I used .X to export and them import into MED with no problem.