I have been trying to add new trees to Fallout NV GECK, but I′ve encountered some problems.

I am able to add a new .srt file from the directory, but I am unable to get the leaf textures working properly. When I load the leaf textures, they show up on the screen as a whole picture, not just the leaves as they are supposed to. So, how do I get the leaves separated from the pictures background, so the background doesn′t show up? When I converted the textures to .dds files, I saved them with the settings DXT1 RGB 4bpp and no alpha. What are the .dds settings that should be used in Fallout textures? Does anyone have any experience in adding speedtrees?