[Texture] Import alpha channel?

[Freeezer]

I'm playing with a model for port to GMOD/HL2 engine and he has several hair textures but they are in .DDS without transparent background so they don't work with $translucent or $alphachannel when I convert them to .vtf. The model bring the alpha channel like a new texture, there is some way to import this alpha channel texture to the main diffuse texture?

https://files.facepunch.com/forum/upload/308715/005161ac-a44f-4c5b-bba6-cbb5bd88818a/igm1.png

If I need do it manually whats the best software for remove backgrounds? or another way?